Bumblebee catfish. They look monster, but they're awesome little miniatures.
Kuhli loaches are awesome, and are best kept in groups. You could put a good bunch of them in a 10, as long as filtration is adequate.
A while back I set up an awesome community tank that I filled with cherry barbs, albino cherry barbs, Harlequin rasboras, pork chop rasboras, and several varieties of danios, focusing on longfins. The variety of colors was a lot of fun, and the pictus cat that was cleanup crew added lots of character.
You could also talk to your LFS about raising monsters- buy a small "monster" (IE: any fish that will outgrow your tank), raise it up a bit, and trade it in for a small one again when it outgrows the tank. There was a customer who did this with some cichlids at the LFS I used to work for. The store loved it, because they sold the larger ones for twice what they sell the small ones for, so they always made extra money from the trade. Thing is, only certain stores will do this, and not with all fish. That could be an exciting tank to show off.