Hey there~
For a 2g hex, aside from a nice bit of rock, maybe some nice button polyps (they stay small and come in a variety of colors too), maybe a couple of featherdusters, what about some candy cane coral?
I would stay away from xenia only because of how big they can get and how quickly they can spread. Same with most mushrooms too. The only fish I can think of that might do alright would be some dwarf seahorses, but they can be very tricky to keep and I don't know if you want to go that route. If you are interested, then check out their requirements here.......
www.seahorse.org
Instead of fish, you could always go with some shrimp or crabs....
HTH
