I like to slice them up and drizzle with olive oil, salt, and pepper. Maybe some basil leaves as well if you have any. Fresh mozzarella (to make caprese salad) is a good addition as well.
Otherwise one of the easiest ways to use up a lot of tomatoes at once is to make pasta sauce. I slice the tomatoes into wedges, about 8 wedges per tomato, lay them as flat as possible in a pan, add a little olive oil, salt, pepper, and any Italian seasonings you have lying around, cover, and simmer on low-medium heat for about half an hour. To get the timing right I usually begin boiling water for pasta as soon as I've started cooking the tomatoes, and by the time the pasta is done the sauce is done as well. Very fresh tasting, 100000x better than tomato sauce from a jar.