I'm surprised no one has mentioned Rewards Network (formerly known as i-dine). Almost all my travel is on Air Canada, but I've accumulated a surprising number of miles on AA from dining. 64K miles in 2007, 52K miles in 2008. (This pales in comparison to Jailer who seems to earn about 200K miles/yr from eating! ) This year won't be as lucrative due to a lack of bonus opportunities, but I still expect to get around 40K miles.

OP, check these out:

AAdvantage Dining Program
Delta Dining Program

Make sure you check out the i-dine/Rewards Network forum for sign up bonuses and tips on how to maximize points earned.