I make a lot of fresh salsa (pico de gallo style) in the summer, but I don't usually think much about the type of tomatoes I'm usuing. Usually I just buy whatever looks best (fresh & ripe) at the farmer's market, so I've used everything from beefsteak and heirloom to cherry and grape. I've been quite happy with the results, but I'm still wondering: is there a "standard" tomato variety for salsa?
A standard tomato implies that there is a standard salsa, which there isn't - but let's stick with your specific case of pico de gallo AKA salsa cruda.
The distinguishing characteristic of salsa cruda is that it uses raw tomatoes - the cruda literally means raw. Since you aren't going to be cooking them, and since water is going to be your primary binding agent, you'll want to use plump, juicy tomatoes that have potent flavour when raw, and that just so happens to be those bog-standard globe tomatoes you see in the supermarket aisles. Of course, if you can get garden-fresh tomatoes, so much the better.
Cherry tomatoes are also a great choice - they're very juicy and a little sweeter than globes - the only downside is that for a chopped salsa (as in pico de gallo), they tend to make preparation much more difficult and messy. If you've got the time and patience, give it a try; cherry tomato salsas taste much "fresher" than those made from globes.
The other common types of tomatoes, most notably roma and pear tomatoes, are really meant more for cooking. That's not to say you can't eat them raw, but they don't have a lot of juice or raw flavour, so they don't make a good base for cruda. Roasted roma or heirloom tomatoes (especially fire-roasted) make a great addition to salsa, but of course, it's not really "cruda" anymore if you cook any of the ingredients.
Do yourself a favour and don't use the plum tomatoes in a can; they're plenty juicy but have almost no seeds and no flavour.
So, all in all, for pico de gallo I believe that regular globe tomatoes are the most appropriate, but any tomatoes with strong flavour and plenty of juice will do.
If we go by the seed companies, the fresh salsa tomato is a variety of plum tomato.
And I agree with Michael -- I prefer plum tomatoes varieties for pico de gallo, in part because they have a lot more 'meat' to them than seeds & gel, and seem to hold up a bit better after they've been salted.