Food is one of the major expenses of any vacation. I typically budget $100.00 per day, or more, depending on the location. It pays to create a list of potential restaurants, both to assist with monitoring expenses, and also to insure that you find quality eating places which feature the local cuisine (important to truly experience the culture of a destination). I start with an online guidebook, like Fodors, and then cross-reference with other sites or guidebooks to develop a fairly extensive list, then check out the menus prior to making a final decision. I also ask the locals, hotel clerks, bellhops, cab drivers, for their suggestions once I am in the vicinity.
I try to keep restaurant business cards in a notebook for future reference, and, of course, I always have my journal to look back at, should we ever travel to the same place again..