Even a small Oscar shouldn't be kept in a 10 gallon. It would easily outgrow it in 2 months, if not sooner.
I set up a tank for a friend of mine with 6 Neons, 4 Fancy Guppies, and 2 Cory Cats, which looked really nice. Sadly, the Gups didn't make it through the cycle. If I was stocking a 10g, I'd probably do one center fish (Gourami or Betta), a small school of tetras/danio (maybe 4-6 fish), then maybe 2 Cory Cats and an Oto or two for algae cleanup.