If you're talking fast food...
Carl's Jr/Hardee's offer a turkey burger that's under 500 calories (less if you aske them to hold the mayo).
KFC has grilled chicken sandwiches that aren't too bad
Chik-fila... most anything on their menu besides fries. As always be careful of how much cheese or mayo.
Taco Bell has a fresca menu. 3 fresca tacos are under 500 calories.
McDonalds only has decent breakfast. Egg McMuffins are 300 calories each (just the egg/cheese/muffin)
For out at Restraunts, like CFD said, most chicken items are fine. If you have the option of salad, ask for dressing on the side, and get oil or vinigarette instead of ranch. If you feel like steak, sirloin is a very lean cut, and a lot of places have started serving sweet potato. Opt for that, with some green veggies. Broccolli being my favorite
And almost all places have a "under 700 calorie section". What you REALLY need to be careful of, is the free crap some of those places bring you. I can't stress how bad for you the breadsticks are at Olive Garden (about 300 calories each IIRC). Free chips and salsa can be pretty devistating too! And always substitute fries for veggies if you can