I have ordered some gift certificates off of Restaurant.com. I got a half-off lunch coupon for about a buck, and it's good for half off your total bill, up to 6 people. I have used a few and saved at least $5 each time. The problem is that there are not many restaurants near me that participate, and you have to read the fine print very carefully for restrictions.
I also always order water out - started for monetary reasons, but I have actually found that I enjoy my food more. If you are going to a fast-food place, order off the dollar menu. You can usually get a sandwich and fries for $2 instead of spening $3 or $4 on a meal. A lot of restaurants have great dollar menus with chili, baked potatoes, chicken fingers, etc.
One more idea - if there are no restrictions, order the kids meal. it's a ton cheaper, and who needs all that bad-for-you food anyway. KFC has an age restriction on theirs if you go in the store, but if you go through the drive-thru you can get it (same with Arby's, I think). If you are trying to watch the fat intake, it's a good way to go both because it's less calories and they often include some better-for-you choices (applesauce, apple dippers, etc.). A lot of restaurants will not let you do this, however.
Of course, you could always eat out less...but what fun is that?
