I have two cards that offer me the best benefits.
One is the Chase Freedom Card (Which now is called the Chase "Perfect" Card that someone else mentioned in this thread).
Their Website Along time ago, this was the Chase Shell (Gas) card, but shell switched from Chase to Citi, so this is what they came up with. Anyway, the benefit is that it gives you 3% back at any gas station and 1% back on all your other purchases, and it's credited immediately to you on your next month's bill. (It's actually 6% rebate for first 90 days)...
The other card I use is the newer Shell Citibank card, which gives you 5% back on gas you get at Shell, and 1% back at anything else. However, they'll credit you back in $$ you can redeem at shell. Not a problem for me because I buy gas every month from shell, but if you're not... then you see the problem. Again though, you get the money immediately the next month.
Anyway, stay away from any cards that make you add up all your rebates until you can redeem them in 50 or 100 dollar increments. Also, my freshmen and soph years in college, I remember alot of cards that would allow you to earn a large % rebate, as long as you carried a balance forward from month to month (this was always in the fine print, and meant that whatever rebate you were getting, was not going to be better than the interest you're paying anyway). Make sure you stay away from those, and the moral is, read everything before you sign.
Good Luck, oh, and I got both of those cards while I was in school.