have you thought about a crab? I had a crab once, they are very elusive, but when you do see them, and see how they change their habitat you cant but feel amused.
Now a hermit crab would work yes, but I was thinking more along the lines of a Halloween crab or maybe a Fiddler crab.
I'd check those out a bit, and they are WAY different and really cool.
further ask on that I guess, I don't truly know if a crab like that is suited for a 10 gal. I'd imagine it would work though.