Curries can be made relatively cheaply as said above, if you have some of the spices already. If you don't, keep an eye out for deals on the pre-made sauces and stock up. Make large portions using chicken, onions, garlic, and a few other cheap vegetables and eat the leftovers for a few days.
Vegetarian meals are also great options, so long as you include plenty of beans/lentils/barley to fill you up. Bean casseroles, bean soup, or three-bean chili are great ways to make large portions without spending large amounts.
Pasta with pesto is cheap, however the parmesan can set you back. Be sure to find a large block and grate your own. I find that adding in your own ingredients helps vary the flavour - garlic, sundried tomatoes, capers, fresh tomatoes, chilli peppers, etc. Not all at once, but one or two just to mix things up.
If the weather's cold (as it seems to be consistently up here), I would opt for classic winter meals - leek, potato and bacon soup, home-made chili, vegetable stew, etc. There are always sales on meat pies at various grocers, which when accompanied by some frozen veg (large bags area cheap) and some potatoes (mashed with garlic, butter, and horseradish) can fill you up for 2-3 meals.
Other than that, just look at what you eat and identify the most expensive item on the menu. Cut that out, and repeat exercise until you're at the bare minimum.
The trick isn't really planning all of this, it's following through. Always tempting to buy beer, wine or a treat when you've been under self-imposed austerity for weeks!