Here are my tips. I'm a vegan with student loans and credit card debt, so I work hard to find cheap, healthy food!
In no particular order:
1) Another vote for beans and other legumes!

I'm a chick pea fanatic myself, but black beans are muy cheap. Beans and brown rice is a dirt cheap, healthy lunch or dinner option. Plus beans last forever in your cupboards.
2) In NYC at least, fresh produce from fruit stands can be surprisingly affordable.
3) I try to eat fresh as much as possible, but I also stock up on frozen spinach, peas, and squash when it's on sale. The frozen stuff is easy to throw over pasta or into a recipe and a lot of the stuff on sale is like a dollar a package - very economical.
4) For breakfast, get a big carton of generic oats. It'll last for months.
5) I'm sure you've thought of this, but pack your lunch for school or work. It's much cheaper and more healthful than eating out.
6) If you have a Trader Joe's near you, you can find some organic food at cheap(er) prices. They also sell nutrition bars (like luna and clif and builders) for cheaper than I've seen anywhere else (again in NYC at least).
7) I don't eat dairy, but I notice that yogurt is on sale a lot (like every 2 weeks at the grocery chain near me.) Usually it's almost half off. This is good if you're willing to be flexible with your brand.
Good luck. I love reading everyone's ideas about this.
http://This message has been edited by mspavement (edited Jun-08-2006).