If you don't already have a travel rewards credit card, now is a good time to get one. That's because credit card sign-up bonuses are 25 percent more generous this year, according to credit card rewards expert Brian Kelly of ThePointsGuy.com. Play your (credit) cards right, and you can earn a free airline ticket -- sometimes in premium class -- for your next trip.

“Travel rewards are the best because savvy travelers can easily get 3, 4 or 5 cents of value per point/mile,” said Kelly. “That’s far greater than the typical 1 cent per point offered by cash-back credit cards.” 

But only 42 percent of credit card users are earning any kind of travel reward points or airline miles, according to a survey commissioned by ThePointsGuy.com and conducted by Princeton Survey Research Associates International. 

Of course, it's important to note that rewards credit cards are only beneficial if you pay off your balance in full every month -- high interest rates can quickly negate any rewards value you may accrue. But if you don't carry a balance and you're not earning travel rewards, consider signing up for one of these cards currently offering hefty sign-up bonuses: 

Chase Sapphire Preferred

Sign-up bonus: 40,000 bonus points after you spend $4,000 on the card in the first three months. 

Reward earnings: Two points for every dollar you spend on dining and travel. Redeem travel through Chase Ultimate Rewards and 11 transfer partners that include major airlines and hotel chains. 

Annual fee: $95, waived the first year.

Barclaycard Arrival Plus World Elite MasterCard

Sign-up bonus: 40,000 bonus points after you spend $3,000 on the card in the first three months. 

Reward earnings: Two miles for every dollar you spend, plus a 10 percent bonus on miles you redeem for travel, on any airline. 

Annual fee: $89, waived the first year.

Citi/AAdvantage Platinum Select MasterCard

Sign-up bonus: 50,000 American Airlines miles after you spend $3,000 in the first three months. 

Reward earnings: Two AAdvantage miles for every dollar you spend on American Airlines and US Airways purchases, 1 mile for every dollar spent on other purchases. This card also gets you Admirals Club membership privileges and a free checked bag on every flight.  

Annual fee: $95, waived the first year. 

Gold Delta SkyMiles Credit Card 

Sign-up bonus: 30,000 miles after you spend $1,000 in the first three months, plus a $50 statement credit after you make your first Delta purchase in the first three months. 

Reward earnings: Two Delta SkyMiles for every dollar you spend on Delta purchases, 1 mile for every dollar spent on other purchases. This card also gets you a free checked bag on every flight.  

Annual fee: $95, waived the first year. 

Capital One Venture Rewards Card

Sign-up bonus: 40,000 miles after you spend $3,000 in the first three months. 

Reward earnings: Two miles for every dollar you spent on any purchase. 

Annual fee: $59, waived the first year. 

Platinum Card From American Express

Sign-up bonus: 40,000 miles after you spend $3,000 in the first three months. But as Brian Kelly points out, certain targeted users have been getting whopping 100,000-mile bonus offers. 

Reward earnings: One Membership Rewards point on every dollar you spend, two Membership Rewards points on each dollar of eligible purchases made when you book using a Membership Rewards program-enrolled American Express Card on the American Express Travel website.

Annual fee: $450, but you also get a $200 fee credit on the airline of your choice, free credit for Global Entry or TSA Pre-Check, free access to lounges and more.