Do you like mushrooms? I find they really help add body and richness to a meatless sauce. Just chop them up, and fry them in some oil with onion and garlic before adding the tomatoes and whatever other flavorings. Also, try adding some wine as well - will add flavor and some tanginess. Red has a stronger flavor, but you can also use white if you want less wine taste. Sometimes I use sherry too. Alcohol really brings out the flavors in tomatoes (but don't worry, all the booze will be gone after you cook it!). And, finally, I always get better results with canned tomatoes rather than fresh, plus it's way easier and cheaper. I like to use the kind that's like whole peeled tomatoes in a thick sauce - squish the whole tomatoes with your hands before you add them, and cook with the lid off to evaporate some liquid.
Oh, and I also like the one Ceit posted - it's very simple but somehow the butter really adds that extra something.
