Best rewards programs for credit card use?

[buffett]

My Discover card (platinum) has no annual fee, gives 1% back, and (as far as I understand the T&C...*please* correct me if I'm wrong here) doesn't have any cap on how much you can get back in one calendar year. (I haven't yet used it to make any purchases, b/c I'm using it as a placeholder for a 0% loan (due in February06, at which time I plan to start using it as my primary card, replacing my $80 annual fee American Airlines Mastercard).)

[deathtoau]

There is no cap on how much you can earn, but there are a few conditions on it. First is that the cashback bonus is tiered; the first thousand you charge is .25% cashback, second thousand is .5% cashback, third thousand is .75% cashback. All purchases over 3 thousand is 1% cashback. The total charges are reset every year so you have to start back at .25% cashback and rebuild your tier level. The second thing is that you can only redeem your cashback award in multiples of $20 so if you don't use a lot of credit, it may take a while to see the result of any award.