For business travelers who fly mostly within the U.S., or to Mexico, the Dominican Republic or Jamaica, the Frontier Mastercard offers quick rewards.

Spend more than $500 in the first 3 months and you'll get 40,000 bonus miles -- enough for two round-trip domestic flights. Other cards typically require spending at least $1,000 to $3,000 to earn that many bonus miles, says Gonzalez.

Plus, for every flight you book on flyfrontier.com, you'll earn double miles. So if you take Frontier Airlines frequently, this card is great, says Gonzalez.

And even if you don't book flights all the time, just one purchase every six months keeps your miles from expiring.