There are two kinds of summer tomatoes: those that are perfect, and all others. The others -- the imperfect ones -- benefit from being cooked (a topic for another day), but the perfect ones are easy: Slice, maybe drizzle with olive oil, sprinkle with salt and pepper, and eat.
Of course, too much of a good thing can be ... well, too much. I love eating minimally-seasoned tomatoes as much as the next person, but after a while, I begin to remember that there are loads of ways to take the fruit in interesting directions while preserving its essential tomato-ness -- all without turning on the stove.
How do you identify a tomato that's worthy of eating raw? Whether you're buying cherry tomatoes, plum tomatoes, or slicing tomatoes -- all largely interchangeable in recipes, by the way -- look for deeply colored (usually red, of course, but sometimes yellow, orange, green, and even brown or purple) skin. Squeeze: Good tomatoes are soft but not so mushy that your fingers leave an indentation. Smell it, too; if it smells warm and fragrant, it's probably good; if it smells like nothing, beware. And when you get it home, do not under any circumstances refrigerate it -- cold air will turn it grainy and bland.
Raw tomatoes, as you know, require almost no preparation. When dealing with slicers and plum tomatoes (not cherry or grape tomatoes), you might consider coring. Just cut a cone-shaped wedge around the core (the rough brown spot, where the tomato is attached to the vine) and pull it out. Now slice or chop as you like, and don't waste the juices expressed by the tomato as you hack at it; pour them from the cutting board into the bowl or food processor you're working in, because they'll considerably enhance the flavor of the final dish.
Cherry tomatoes are among the most reliably sweet and juicy raw tomatoes, even before and after peak tomato season. They're especially delicious when halved and tossed not only with the expected olive oil, etc., but with quintessential Asian ingredients: soy sauce, sesame oil and Thai basil. The soy and sesame combine to give the tomatoes a deep, rich saltiness.
You can take tomatoes in a sweet direction, too (which may sound odd, until you remember that the tomato is a fruit). Puréed with mango, melon, peaches, or a combination, along with olive oil, vinegar, and stale bread, they turn into a sweet-yet-tangy, entirely refreshing gazpacho.
For something a little heartier, consider serving raw tomatoes with pasta. Roughly mashing ripe tomatoes with garlic, olives, capers, and anchovies turns them into a summertime approximation of puttanesca sauce. You can leave out the anchovies if you like, of course -- but I find that the tomatoes' sweet juiciness takes away the fishy edge. Granted, you do have to turn the stove on to cook pasta for this recipe, but it's worth it.