I pretty much follow Scylla’s recipe, but experiment with different hot peppers (no bell pepper though). Sometimes I’ll put in grilled cactus (nopales). To me it adds nothing to the flavor, but sounds bad-ass to say your salsa has cactus.
I’ve yet to try and make my own because the stuff from the local Mexican place is so good, and they, up until recently, gave it out two or three cups at a time with any meal.
Bell pepper is fine, but not necessary. I’ll put it in if I have some, especially if I needed a partial pepper for another purpose.
For something that’s name translates directly as “sauce”, you’re being awfully specific. Mexico is a big place, and so is the US Southwest, both of which can legitimately claim to make authentic salsas of all sorts.
I mean, there’s salsa fresca and salsa verde, both of which are totally authentically Mexican, and only one is tomato based. I’ve had cooked salsas with a beef broth base that was served hot with chips (surprisingly good), and salsas made from almost straight chiles. Some are garlicky, some are pretty much like Mexican marinara sauce, and some are spiced, as well as having the usual tomatoes, onions, chiles and garlic.
Then there’s kind of out there stuff (from our perspective) like salsa de cacahuetes and arbol chiles (I’m assuming as the arbiter of all things salsa, you can read Spanish)
Basically I’m reinforcing what others like pulykamell, scabpicker and silenus have said.
Okay, while we’re on the topic. People often misunderstand the difference between salsa and hot sauce. Hot sauce is a condiment, salsa is a meal. Good hot sauce makes you sweat as does good salsa. I’ve searched everywhere and finally found an a salsa that rivals my daughter’s hispanic in-laws home made salsa. El Campestre “Salsa Roja.” If you like hot salsa, this is the absolute best.
Out of 25 posts, only 3 mentioned garlic, and then only in passing. Garlic is as essential as the tomatoes, cilantro, onion, and lime.
The quesadilla place a few blocks from me has their extra hot salsa made with peanuts, as above. Delicious stuff. It’s not really chip-dipping salsa, but excellent on all sorts of meats.
As a fellow Texan, I will echo this again. There are many types of salsa, and some of them are just fine from a jar. Not all salsa is trying to be pico de gallo.
Nah. It’s nice, but certainly not essential. (ETA: I’d guess about half the places around me, perhaps more, don’t use garlic in their salsa fresca/pico de gallo.)
Garlic, which I love nearly as much as life and bacon, can be used in a salsa but is not necessary. Roasted garlic is even better.
You know who else puts bell peppers in their salsa?
Pace. (What? Who did you think I was going to say?)
Explore the world of green chiles, my friend. Anaheim, poblano and Hatch (or New Mexico) green chiles, especially roasted, are an essential ingredient in all Mexican food.
I’m just hoping Scylla never goes to Mexico. In particular, he should never visit different regions of Mexico. Much better to just keep fantasizing about it from this side of the border. 
For myself, there is no such thing as a bad salsa. I like all of it, provided that it’s not overly spicy or too heavy on cilanto. (I’m one of those genetic mutants that tastes cilantro as being like soap.)
My wife makes a fresh salsa that the OP would love. She also makes a partly blended, cooked spicy salsa that is to die for. Both of them are salsa. I pick the salsa that complements what I’m eating.
Our local place makes a great sauce that we pick up any time we make enchilada or taco salads. The rest of the time I either whip up a fresh batch of pico de gallo or rely on one of the myriad jarred sauces available around here. I’m partial to Mrs. Renfro’s.
Big difference between green chiles and “bell peppers” though, at least in flavor and texture.
On the subject of weird salsas, there’s a local roast chicken place (“Pollo Regio”- I think it’s Mexican-style) that has a green salsa that from everything I can google about it, consists of very finely blended cooked jalapenos, oil and salt. Sort of a jalapeno mayonnaise-ish/aioli-ish kind of thing. It’s awesome.
You may have misunderstood: “Pace” was derogatory. 
I see that there are several points that have been brought up multiple times by various worthy posters. Rather than handle them one by one with direct quotes I will paraphrase them and respond en masse. This will serve the dual purposes of being more efficient, and more importantly enable me to set up straw men which will be much easier to knock down than if I actually attempted to respond to valid and thoughtful objections:
- Who made you the King of Salsa?
This was not something I chose. Moses did not make the 10 commandments. They were thrust upon him to deliver to the Israelites. Like Moses, I would have preferred that this burden had fallen to another.
- Salsa just means “sauce.” Why are you being so rigid and exclusionary? Why don’t you just lighten up?
Regardless of the etymology of the term, “salsa” now means the the red chunky stuff you dip tortilla chips into. Similarly “car” can etymologically be any sort of compartment for transport but when I say “car” we all know that I am talking about the the thing with four wheels and a steering wheel that you drive down roads.
They is some confusion as the Spanish word for Salsa as I’ve described it is “salsa,” which is the same word they use for sauces in general. It would have been nice if they had come up with some kind of name true salsa from generic sauce. I know they tried with “pico de gallo.” But that didn’t take. Nobody goes to a party and says “try the Pico de Gallo.” The say “try the salsa.” As Led Zeppelin reminds us “sometimes words have two meanings.”
If I was writing in Spanish and used the word “salsa,” perhaps you might be confused as to whether I was referring to Bernaise or Hollondaise. Since I am writing in English and use the word “salsa” and not “sauce,”. I am clearly referring to the fresh red chunky stuff. You are just being pedantic and difficult. No salsa for you.
- What about my delicious salsa verde?
Salsa verde is simply Spanish for “pesto.” As everybody knows, they don’t have pine nuts or basil in Mexico, so the just use chiles. They substitute chills for everything. This is not a bad thing. Salsa verde is just failed pesto sauce that became a success in its own right in the same way that the Rolling Stones became successful by failing to emulate the blues, and ended up creating something new and worthy in its own right.
- I like or use cooked ingredients and tomatoes
Congratulations on your marinara sauce. See #3.
I’ve described several extraordinary near supernatural powers that true salsa conveys unto the worthy acolyte. I’m sure all you other varieties of sauces are quite yummy, but do they make you sexually desirable the way true salsa does? Can you eat infinite quantities and still lose weight? Does it work, as a condiment, a side, a salad, a main course, an appetizer and as something yo put on a chip Simultaneoulsy?
I didn’t think so.
I’m with you on the chunky part. It’s harder to load up a tortilla chip (or totopo, if you’re lucky enough to have Xochitl at your supermarket) than with smooth.
I use crushed tomatoes and throw in white onion, jalapeno and sometimes habanero pepper diced super-tiny, garlic if I have some on hand, salt, and chopped fresh cilantro. That’s the way they make it at our local high-class Latino restaurant. It’s owned by Peruvians, so maybe it’s a Peruvian salsa thing. Proportions don’t seem to be written in stone: as long as you don’t go crazy with any one ingredient, it tastes great.
Salsa is for sure one of those areas where nothing much is canonical. There are a gazillion different types, each one open to individual interpretation. It’s really pretty hard to go wrong IME.
I agree. Hot sauce is a liquid condiment. Salsa is more of a topping. Both can be hot. At least this is how it’s used in these parts.
Salsa picante hot sauce is really “hot sauce.”
- No true salsa has bell peppers.
Yes they do. I posted first. Neener.
You could put corn in it if you wanted to, but I know of no Hispanics who put bell peppers in salsa. But then, there’s no rule against it.