I make two kinds of salsa: 1) cooked and canned and 2) pico de gallo.
The pico is much, much simpler to make. I don't have exact measurements, as I make varying amounts depending on who I expect to be partaking in it (and I taste as I make it), but for a small party, I'd probably do something like this:
2 lb tomatoes (diced)
1 lb white onions (diced)
4-5 mediuim-sized jalapenos (diced)
1/4 cup chopped cilantro
Juice of 2 limes
1-2 tsp salt (start with 1 tsp and add more if desired)
Mix ingredients together in a bowl and let sit for about an hour (if you can help it!) to let flavors marry. The great thnings about pico de gallo is that it's a fresh recipe, so you can mess with the amounts of these ingredients in whatever way you like - just chop a little more of this or that and add until it's how you like it.
My canned salsa is a bit more involved, and I've only been making it a couple years so I need to refer to my recipe (which I don't have on hand). It *is* good though!