Ok, I eat out as much as anyone (the one reward I allow myself while on the road), so here is my take:

1. Enlist in an iDine/Dining Rewards program. This costs nothing and while the restaurants are limited, the 10 miles / $ makes this a no-brainer. You don't have to do anything at the restaurant other than eat (or drink) once you have registered your c/card. Plus, the promotions are sometimes a huge perk: check out United's 25,000 mile bonus for spending $125 / month for July - December! I'm all over that. I've found some really nice restaurants that I would never have found w/out this program.

2. Other than that, I don't have a favorite card but instead, I keep an eye out for the best promotion offered by the cards that I already have. I have a Hilton Hhonors card that pays 5 points / $ but I have so many Hilton points that I seldom use this save for Hilton stays (where it pays 10 points / $). My Discover will sometimes get me 5% cash back on dining purchases and even though their merchants are getting stingy, this is a good deal. I also love my Southwest visa because that earns me tickets that I can actually use!

I've found that you just need to be proactive as some of the promotions require advance registration (e.g. the United Dining promotion and Discover promotion discussed above).

Oh, also, I recommend checking out chowhound.com (not sure if we are supposed to plug other sites or not!). It is a great bulletin board site where travellers and locals point out some of their favorite restaurants in all areas. I've found some decent meals with the use of this site.

Chow Down!