My wife got me a large grill basket (wire basket type), and I have never used it until this year. I had a bunch of roma tomatoes I grew, so I experimented with some recipes, until I finally got a great salsa.
I would halve about 12 good size roma tomatoes, and lay them in the grill basket skin side down. Halve about 3 jalepeno's (seed them) and put them skin side down. cut one large onion into quarters add them to the basket. Add about 4-5 cloves of garlic (leave the skin on) to the basket.
I cooked all of this over medium heat on a charcoal grill until all of the skins started getting charred. The grill basket makes it easy - you don't loose anything and you can place and remove it all at once.
I would squeeze the roasted galic out of the skins, and put them and the jalepenos in a food processore and hit pulse a few times. Then add the onions and do the same - you don't want to purify them, just a good chop. I would take the tomatoes and spoon out the pulp and sees (just throw those away or they will make the salsa too watery). I would add the tomatoes, a little less than a quarter cup of cilantro, some salt, a couple dashes of cumin, and juice 1/2 a lime in the food processor and pulse it a few times.
It really is the best salsa I have ever had, and even better after it is refrigerated. The charred skin from the tomatos and chiles add a ton of flavor.
I also substited two of the jalepenos with a habenero and it was outstanding. It had a little more kick, but roasting it first takes a good deal of the heat out from the peppers.