If they're large planters, some varieties of bush beans, smaller tomatoes, and definitely peppers!
Bok choy works well, especially if you harvest it young & small for stir-fries, etc.
You CAN grow root vegetables in those containers (I hauled a 4-lb. sweet potato out of one of mine one year!) but they take up too much space to really be viable.
Beets will work if you grow them mostly for the greens, and keep cutting them. You will get a few good roots, too, but again, space is an issue for them. Add a little more sand to your potting mix if you go with them.
A lot depends on the growing season where you are, too. Fennel works nicely in containers if you have a long enough season to let the bulb mature.
If you have space and support to let them run around some of the vining summer squashes and cukes will probably work. I'd try lemon cukes, they don't need as much support. And some of the "pattypan" summer squash varieties, ditto.
helpfully,
Bright