Following are the Oppenheimer's top equity ideas for May. The stocks are based on their view of the company's fundamentals in the context of current market conditions.

Visa (NYSE: V):

Oppenheimer said it is highly attracted to Visa's powerful brand, its vast global acceptance network and its strong business model.

"We believe the company is well positioned to benefit from the long-term secular shift from paper (paper currency) to plastic (electronic payments), consumer spending growth and increased globalization," analyst Glenn Greene said.

The company has a dominant debit franchise in the US, which the analyst believes buoys near-term growth.

CheckPoint Software Technologies (NASDAQ:CHKP)

CheckPoint remains the brokerage's top pick driven by the secular shift to security appliances and the continued strong acceptance of its blades strategy. In addition, there is further traction in the end point market now that McAfee has been removed as a competitor (by Intel's acquisition). With $10 of cash per share and expected continued double-digit growth rates, valuation looks compelling at current levels.

Qualcomm Inc. (NASDAQ: QCOM)

Oppenheimer said its Outperform rating on Qualcomm reflects a still-expanding CDMA market, opportunity for share gains, an improving product portfolio with the company's single-chip integrated solutions, Snapdragon and Gobi platforms and the potential of the company's new Mirasol display technology.

Teradata (NYSE:TDC)

Teradata is levered to the attractive secular trends of increasing data creation/storage and accelerating adoption of BI analytics. Revenue growth is likely to continue to recover as IT spending rebounds and enterprises are increasingly willing to open the checkbook on larger ticket items. Products are extremely "sticky," and sales to existing customers are relatively predictable.

Teradata is a leading provider of enterprise data warehouse solutions that integrate a customer's disparate data into a central depository, enabling better data consistency, improved analytics and lower costs.

Broadcom Corp. (NASDAQ:BRCM)

The brokerage views Broadcom as a core holding and one of the best-positioned large-cap semi names to drive top-line growth. Broadcom's diversified business should benefit from any pickup in enterprise spending, while the long-awaited baseband ramp represents a primary top-line driver in 2011/12. Combo chips (WLAN, BT, GPS and/or FM) still surpass expectations and appear poised to continue momentum in 2011/12.

Despite some catch-up spending and acquisition pipeline, the brokerage looks for management to make good on its promise to drive EPS growth in excess of top-line growth.

Comcast (NASDAQ:CMSCA)

Oppenheimer thinks the worst is now behind Comcast from both telecom competition and the economy (evidenced by the strong results during the last three quarters).

The brokerage believes the recently-closed NBC Universal acquisition will be highly accretive, and will benefit from an improved advertising environment. The company is now past regulatory uncertainty which pressured the stock somewhat in 2010, as the industry and the FCC came to a mutually-acceptable agreement on the possible regulation of broadband lines as a telecom service.

Citigroup (NYSE:C)

"In our view, C shares are attractively valued at .94x tangible book value given C's good leverage to improving US consumer asset quality and good global growth prospects," analyst Terry McEvoy wrote in a note to clients.

 In addition, McEvoy view Citi as having less exposure to private-label mortgage put-back risk, and to lower than average exposure to the Durbin amendment debit card price controls.

"While we believe that the industry will in general offset the impact of price controls with other charges, we think there is risk in implementing any change in pricing schemes, and Citi has less of this risk than most peers," the analyst added.

United Rentals (NYSE: URI)

The brokerage believes URI will gain market share as it is turning offensive, while smaller, regional peers are still on the defense. With used equipment pricing, then utilization, and now rental rates firming, the brokerage believes URI is well positioned for 2011 growth.

Elizabeth Arden (NASDAQ:RDEN)

The brokerage said the company should benefit from the ongoing shift in consumer traffic out of department stores. Its global re-engineering initiative should continue to drive significant margin expansion and earnings growth.

Oppenheimer expects fiscal 2011 gross margin to expand 260 bps, to 47.5%. The company is also focusing its attention on European market shares gains. This is a long-term opportunity, since its current market share today is only a little over 1%.

Williams-Sonoma (NYSE:WSM)

Williams-Sonoma continues to represent one of the most compelling investment opportunities among leading mid-cap hardlines stocks, the brokerage said.

Sales and margins at the company have improved markedly over the past several quarters as it has executed successfully on a significant business model transformation and capitalized on improving demand dynamics within the home furnishing sector.

"We view the WSM story as being far from over. Recent data suggest that the sector and macro backdrop continue to turn more accommodative. We think the shares have yet to fully discount prospects for much improved earnings power at WSM," analyst Brian Nagel wrote in a note to clients.

Urban Outfitters (NASDAQ:URBN)

The brokerage believes there exists significant upside potential with limited downside in the shares of Urban Outfitters. The shares are attractive at current levels, given domestic and international growth opportunity, best-in-class CEO, significantly improved open-to-buy positioning and unique product assortment.

Tesoro Logistics Partners (NYSE:TLLP)

Oppenheimer believes Tesoro Logistics represents the first opportunity in years to own a 100 percent fee-based (low-risk) pipeline Master Limited Partnership (MLP) with significant dropdown and organic growth potential early in its life cycle.

"We forecast double-digit distribution growth CAGR for the next several years as TLLP expands organically and completes acquisitions. Assets include a large crude oil gathering system in North Dakota and Montana that provides exposure to Bakken formation growth," analyst Bernard Colson said.

"We believe the Bakken is in the nascent stages of development and that TLLP provides one of the most concentrated ways to invest in Bakken development," Colson added.

Marathon Oil Corp. (NYSE:MRO)

Analyst Fadel Gheit believes the upside potential in Marathon Oil shares is greater than the downside risk from sharply lower oil and gas prices. The surge in oil prices has significantly improved the company's upstream segment outlook, especially for its non-conventional oil projects in Canada and the Bakken Shale.

FirstMerit (NASDAQ:FMER)

At a recent industry conference, management was the most upbeat among presenting banks for commercial loan growth in fiscal 2011, given its solid loan pipeline and an increase in utilization rates in the first quarter. Management has a solid record of acquiring both failed banks and Chicago branch networks, and the company is likely to do more deals, which could provide a catalyst for higher earnings estimates.

Questcor Pharmaceuticals (NASDAQ:QCOR)

Oppenheimer continues to expect strong growth in the second quarter from Acthar, driven largely by growth in MS Flares, which exhibited 40 percent quarter-over-quarter growth q-o-q in the first quarter.

"We believe the company has continued to more than adequately account for Medicaid reserves and anticipate any overhang from this to be completely removed by YE11," Chris Holterhoff wrote in a note to clients.

United Therapeutics (NASDAQ:UTHR)

The brokerage favors United Therapeutics ahead of key phase III FREEDOM-M and FREEDOM-C2 trial results for oral treprostinil in Pulmonary Arterial Hypertension expected in June and September, respectively.

"Based on our physician discussions, we believe the use of dose titration in the trials will lead to improved tolerability and, consequently, a substantial 6MWD benefit. Additionally, strong trial powering and management-reported low dropout rates further support a high probability of success in the two studies," analyst Bret Holley wrote.

Life Technologies, Inc. (NASDAQ:LIFE)

Life Technologies is one of the leading providers of life science tools, and the brokerage sees two additional areas that could provide significant upside potential.

First, LIFE has significantly enhanced its investment and product cadence in next-generation sequencing, where there is substantial and under-appreciated growth potential ahead. Second, the company's expansion into the $1.4 billion flow cytometry market provides another differentiated growth platform.

CIGNA Corp. (NYSE:CI )

The brokerage believes CIGNA is an attractive investment opportunity due to its exposure to strong growth areas, relative protection from healthcare reform, and diversification into a number of products. In addition, the company has a large international presence, which should also be safe from reform. While the company also has some risky exposure regarding its VADBe and GMIB businesses, it seems to have them well under control at this point.

Endologix (NASDAQ:ELGX)

Endologix has performed well in recent months, appreciating over 12 percent year-to-date versus 7.5 percent growth in the S&P 500.Near-term drivers include US approval of the low-profile AFX, the rollout of new EU PowerLink sizes, and the company's building salesforce.

Eaton Corp. (NYSE:ETN)

Eaton shares have been weak of late despite strong fundamentals, including a solid first quarter beat and full year guidance raise. The company has demonstrated signs of global share gain in the Truck, Hydraulics, and Electrical sectors, and with a healthy mix of longer cycle exposures (Aerospace, Electrical) to complement early/mid-cycle exposures (Truck, Auto, Hydraulics). Margin execution has also been solid, with material runway on the heels of substantial restructuring and acquisition integrations during the downturn.

IDEX Corp. (NYSE:IEX)

The brokerage has confidence in IEX's long-term outlook for mid- to high-single digit organic growth, but believes near-term expectations remains conservative and could support upside. The company's balance sheet remains solid, and management is targeting $350-400 million in acquisitions for the year.

Vistaprint (NASDAQ:VPRT)

Vistaprint uses the Internet to sell premium-quality printed products at highly competitive prices to small businesses, and is uniquely positioned to increased margins as the company's customer base grows and marketing costs decline per new customer.

Oppenheimer expects Vistaprint's revenues to grow by 19 percent annually through 2015 and are bullish on the company's prospects, driven by the company's demonstrated ability to leverage its technology and databases to significantly lower cost of print products, and potentially market more effectively.