Lots! Green beans, kale, Swiss chard, zucchini & other summer squashes, beets, oakleaf & other slow-to-bolt lettuces, carrots, radishes, cucumbers, "early" cabbage, broccoli, all sorts of "Asian" greens...off the top of my head. Probably more.
Addendum: Tom's note below is absolutely right, but most vegetable seeds germinate right through the summer here in central New Hampshire. Here's a good chart listing minimum/maximum and range of soil temperatures for germinating various vegetable crops: http://bit.ly/12Vo0af (Broccoli would be the same as for cabbage and cauliflower.
It's also important to choose varieties with care; look for salad crops described as "longstanding," "slow to bolt," heat-tolerant, and/or "withstands adverse conditions." Choose broccoli, root vegetables, green beans and summer squashes that mature quickly.