Does anyone know Neville's patronus?

It has never been revealed, in the books, movies or by JK herself :)

hm. it doesn't say so in the books or movies, and his just disappears without forming completely. jo herself hasn't revealed it either. but i would expect it to be a badger, toad, tiger, or some other animal that represents him.
~potternerd~

I know for a fact he can produce a corporeal Patronus. You see it in OOTP. It bursts from his wand, making him stagger, and trips Ron. From what I could see and hear, it is a canid of some kind.