I usually buy the prepacked frozen veggies for mine, which are a mix of spirulina, spinach, and peas. Additionally I buy the little algae discs for bottom feeders, they eat them at will. Usually they steal the algae discs from my mango pleco!!
Zucchini! I love it and so do my fish.
Cucumbers are eaten as well though being that they hold so much water a quite a bit of sugars they should be fed only a little at a time or remove any leftovers a few hours after introduction. The skins aren't popular with the fish either. However with zucchini, some of the fish actually prefer eating it skin-first.
Carrot, steamed or lightly boiled. Romaine lettuce, fresh.
That's about all I use.