Is Neville's Patronus ever revealed. If so, what was it? I can't seem to remember.
Hermoine Jean Granger
Neville's patronus hasn't been mentioned in the books so, you have free reign with that.
I think that his patronus would be something which would be consistent with his personality/his traits. I see it as something shy and gentle and not very expressive, in other words, something similar to his pet, a toad.
No, personality traits are what determines one's Animagus. To find one's Patronus, you have to consider what animal the person might view as a protector.
For example, Neville's friends were always really dear to him, maybe some kind of pack animal. Of course, Herbology was the one class where he never felt like a failure, so maybe a bee or a butterfly or a hummingbird would also work.
Let your imagination fly!