1. I wrote a contract out specifically stating the "rules" and signed it. I taped it to the fridge. Believe it or not this really helped because there were clearly defined limits with no grey areas. Also, everytime I would restlessly head over to the fridge to grab a snack, the contract would be right there to snap me out of it.
Related to this fine idea, I've discovered that I respond better to telling myself "you don't do that" as opposed to "you can't do that." There are lots of things I don't do—drink, smoke, be nasty to people, run red lights, run around nekkid—so if I think I want to eat brownies in the middle of the afternoon, well, I remind myself that other people might, but I don't. I dunno, saying "can't" just tends to make me grumpy, like I'm being deprived.
Related to eating brownies in the middle of the afternoon: Know your triggers/weaknesses, and deal with them accordingly. Lots of people say that they are prone to munching on snacks all evening while watching TV or reading. I generally don't want anything to eat after dinner (and I don't like to eat after 8:00), but man, I could sit in my office and stuff my face with pretzels and York Peppermint Patties all damn day long. My office is tiny and windowless, and sometimes I just...chafe. I seem to struggle especially with wanting to snack in the morning, for some reason. I managed to not do that all through Lent (non-religious Lent) by reminding myself that I don't eat between breakfast and lunch. Some people might, but I don't. I need to regain my adherence to that rule. **sigh**
One more: A lack of variety might work for you. I don't like to go out to lunch (and I really don't like to do during the school year, when the box office is open), I don't like to eat a large or heavy lunch, and I can't be arsed to think up varied menus and prepare stuff. I have a little fridge in my office; every day I eat an apple, some carrots, some snap peas, a string cheese, some nuts, and some pretzels. (There's variety on the plate, anyway.) I'm still working on a good standard breakfast; current experiment is a schmear of peanut butter on a toasted whole-wheat English muffin and a glass of skim milk.