Probably nothing longer than 2 or 3 inches. Mosquito rasboras are good (schooling fish). Honey gourami are also good for a 10 gal. Really not too many things are suited for a 10 gal. A few guppies can be kept in one. Generally if you want big fish, get a huge tank. 10 gal tanks are the smallest I keep because so little is truly suited for them.
+2 to what is said. I have a Dwarf Neon Grouami that I had in a 10g tank, he was so much more happy when I switched him to the 29g community though. I wouldn't put fish that grow more than 2" in a 10g tank, as most of them need groups of 5.