At the height of the economic boom, commercial banks and investors gorged themselves on real estate, building unsustainable towers of debt that finally collapsed in 2008. But with the housing market improving, financiers are returning for second helpings.

Several prominent firms, including Amherst Securities Group, Paulson & Co. and Colony Capital LLC, are eyeing acquisitions of eight Fannie Mae-owned housing portfolios, totaling 2,500 units and valued at $320 million, reports the Wall Street Journal.

But unlike in the previous cycle, these properties won't be sold to buyers with subprime mortgages. Instead, they are to be converted to rental housing, in hopes of unclogging some of country's excess for-sale inventory, and could form the basis of a larger program to relieve the housing market. But the long-term success of the program has its uncertainties, as Fannie would likely have to sell a bulk of properties at a discount, a significant downside as it seeks to repay taxpayers.

For investors, however, rental housing represents a tantalizing opportunity.

Factors that pushed Americans to buy in recent yeasrs -- particularly the availability of cheap credit -- have now reversed, with mortgage underwriting standards tightening and down payments escalating. The economy remains anemic and threats of high oil prices and the euro zone crisis create more uncertainty, pushing more people to rent in lieu of buying. And home prices, which had reliably appreciated since the Great Depression, continue to drop throughout the country, further discouraging the market.

These trends have driven rental vacancy rates around the country to their lowest levels in a decade. And in desirable locations like New York and San Francisco, bidding wars have even erupted over apartments.

As a result, one of the most infamous tales of the bust is getting a surprising epilogue. The estate of Lehman Brothers, whose 2008 implosion had much to do with its overleveraged real estate acquisitions, is now locked in a competition with mogul Sam Zell for control of Archstone, the apartment giant that controls more than 70,000 units of rental housing in the U.S.

Sam Zell's Equity Residential (NYSE:EQR), a publicly traded real estate investment trust, is seeking to buy a 26.5 percent stake in Archstone from creditors Bank of America and Barclays as the first step of a full takeover of the company. But Lehman, which now owns 63.5 percent of Archstone, has the right of first refusal and may match Equity's bid. Deadlines for the deal are in April.

Real estate investment trusts, which own retail, office, industrial and rental properties and rent them to generate cash, have also benefited from tight vacancy rates in hot cities. Major apartment landlords including Equity and AvalonBay Communities Inc. (NYSE:AVB) saw a rise in their fourth-quarter funds from operations, a measure of their ability to generate cash from real estate.

And in perhaps the strongest sign that investors have returned to real estate, the U.S. Treasury Department announced Monday it had sold a portfolio of crisis era mortgage-backed securities for a $25 billion profit

“The successful sale of these securities marks another important milestone in the winddown of the government’s emergency financial crisis response efforts,” said Mary Miller, assistant secretary for financial markets. “This program helped support the housing market during a critical moment for our nation’s economy and delivered a substantial profit for taxpayers.

The next chapter of real, sustained recovery hasn't arrived. But for some canny players, profits have already returned.

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