A basic recipe that we use is at eat Japan
Tonight's tempura included carrots, mang tout, green beans, turnip, mushrooms, and some random squash that i thought was kabocha but was white in the middle, so no idea what it was!
I also wanted to stick some beetroot in there, but we already had TONS of chopped veggies at that point, so I didn't bother. My husband wanted brocoli, but we didn't have any.
more veggie ideas here: http://en.wikipedia.org/wiki/Tempur