I never make it the same way twice, man, but I usually do something like this -
*~8 roma tomatoes, diced. (maybe 1, 1 1/2 pounds) A serrated knife makes this easier.
*maybe 1/2 a small onion, finely chopped. I don't like a lot of onion in my salsa so you'll probably want to add a little more here. Sometimes I'll gently saute them to further mellow them out.
*2-4 cloves of garlic, finely diced or pressed
*cilantro - generally I'll add 1/4 to 1/2 a head, chopped, sometimes more. Again, it depends on mood.
*small number of whaever spicy chilis I happen to have. With jalepenos, I'd start with 1, then add more, tasting as you go
*salt to taste
*spices to taste
That's sort of the "skeleton" of a salsa. You adjust and add to it by taste from there. For example, eric seems to like a sweet salsa, while I like savory. So, I usually skip the lime and bell pepper, and use less onion. I also disagree on salt to an extent - that's not necessarily a bad thing, especially if you're dicing everything fairly fine.
Another thing we've been doing lately is adding half the tomatoes and all of the onion and garlic to a food processer, blending quickly for maybe 20 seconds, and then pouring it back into the bowl and adding the rest of the tomatoes and other ingredients. This gives a more substantial "body" to the salsa - diced fresh, this will give you a liquid that's basically water, just the juice from the tomatoes. Blended and then with additional tomatoes added in, this willg ive you a thicker liquid. It's a matter of taste.
As for spices, generally I'll add cumin (probably at least a teaspoon, maybe more) and some other form of ground pepper - definitely some fresh-crushed black, plus maybe some dried ancho chile powder or cayanne powder or something.
You can also add damned near anything - we've had good luck with adding mangoes to this basic structure.
Salsa is really awfully easy to make - the hard-yet-fun part is tailoring it to your tastes.