This is my favorite recipie. I compiled it from several sources and tweaked it until it came out just right. This recipie is family-sized (My wife and I have five kids), so if you use my measurements, you'll need a very lage bowl.
1 white onion
6 Jalapenos (with seeds)
2 chopped Anaheim peppers
1/3 cup of white wine vinegar
1½ tablespoon of lime juice
Two 6oz cans of tomato paste
½ cup of chopped cilantro
1 ½ tablespoons of salt
2 tablespoons of chili powder.
1 to 2 cloves of garlic (a little goes a LONG way)
1 chopped avocado
You can mix all this up in a blender, but the tomatos turn frothy, and the whole thing comes out like runny ketchup. I prefer my salsa chopped. I have one of those hand-crank food processors that does a perfect job.
Some recipes mention that you should peel your tomatoes, but I have noticed no difference in either taste or texture. To peel a tomato, cut a cross in the bottom with a very sharp knife, then submerge the tomato in boiling water for about 45 seconds. After you pull it out, the skin will come right off.
Some recipes also say that the tomatos should be seeded. You can do that if you like, but it will make the salsa very chunky (a real Mexican would call it pico de gallo). I leave the seeds in, that way I don't need to add water.
Two magical ingredients are lime juice and vinegar. Vinegar enhances flavor, and also acts as a natural preservative. Lime juice adds a little zing.
A third magical ingredient is salt. Add it in a little at a time. Remember, once it's in there, there's no turning back. Salt also brings out the flavor.
The fourth magical ingredient is cilantro. It adds that special je ne sais quois (I'd render that in Spanish if there was one).
You can play with the heat by adding more jalapenos. I find that this recipe is very hot when first made, but that the heat declines after the salsa has sat overnight. Another option to add heat would be to throw in a couple of serranos, which are quite a bit hotter than jalapenos.
So give this a try, and let me know how it comes out!