As a graduate student with almost no set schedule, it's *really* hard to get things done right. Luckily I have an office on campus where I spend most of my time and a kitchen area just down the hall. I keep some bowls here in my office and some silverware, and warm up some soup each day for lunch. Throw in a diet soda and that's $3 for lunch, much better than $10-12 eating out. Every once in a while, we'll go out for sushi or some Thai, but I've really reigned in on the lunch aspect.
Edit: while soup everyday can get a little bit boring, I do always think about how much money I'm saving, how many calories and fat I'm avoiding, etc. So there can be other things that motivate you other than having a tasty lunch - you can be satisfied by an ordinary cup of soup. There are actually some really nice soups out there, by the way - try some of Amy's organic stuff. I'm not an organic kinda guy, but they're much better than most Campball's stuff.
And yes, I've been there before - I do believe that I've had fast food at least once a day for at least 3 months. It's crazy, and it sounds stupid and irresponsible, but when you're in the middle of it, you're more worried about grabbing a quick, easy dinner than you are about thinking about how often you've been grabbing greaseball burgers. And there's this huge salt-dependency thing that I've heard other people talk about, but I certainly think is true: once you start eating out too often, your body really starts craving that rich and salty, greasy food. You have to kinda get sick of it before you break out of the pattern, though.
So, my best advice to the OP is to set aside 1hr every other day (like someone else suggested) and spend some time - and this can actually be fun - researching some recipes. Stop by the grocery store on the way home, pick up what you need and get out of there without buying that 2-for-1 special on Oreos. Go home, cook your food, enjoy it with a beer watching some TV, then spend 15 minutes cleaning up afterward and saving the leftovers for lunch or tomorrow's dinner. Speaking of which, one thing I enjoy is picking out a dinner to go with a nice beer you have.
I'm not sure if this is peculiar to me, but there's a sense of satisfaction (more like a sense of "i'm not acting like a slob!") when you clean up after you've made your dinner and taken care of your leftovers for the next day. Besides, if you leave your mess for later, it weighs on you and in my opinion, sets up a mental block for future cooking, making it almost impossible to get a cooking routine set up.
It helps if you have a buddy or a girlfriend to do this with, by the way.