3 large tomatoes, diced
1/2 - 1 whole onion, diced (red or white, I tend to go red)
1/2 - 4 desired chili peppers, (jalapeno is a safe bet)
3 cloves garlic, minced
1 large handful cilantro, finely chopped
Juice of 1/2 lime (lemon also works)
Salt and pepper
Combine tomatoes, onion, chili peppers, garlic, cilantro, and lime juice in a medium sized bowl. Season with salt and pepper to taste. Adjust cilantro, and lime juice to taste.
Of course you could also just toss it all in a food processor for a more liquid-y salsa.