Pygmy cories (corydoras pygmaeus) could work too.. they stay very small (a little over 1") but don't stay on the bottom as much as most cories, they swim all over. . Salt And Pepper cories (corydoras habrosus) also stay small (about 1-1.5" as adults) if you get the right fish, but I think they are often mislabeled in stores (I'm not sure the ones at petsmart at the right species for example, because I've seen them at about twice the size they should grow to be.. at my LFS the habrosus are teeny tiny, all the other cories are bigger).
Otos are great too but they do much better in schools. I have 15 in my 55 gallon and they swim all over the place and are super active.. I love watching them. Keeping just a handful in my smaller tanks I never saw them move around much and I never did get any to live longer than a couple of weeks before they'd die. I paid more to get my current ones from my LFS instead of petsmart, and they were in much better condition (and some of the ones I got were also tank raised by a customer of my LFS, so I know they didn't get poisoned before they were collected, which is leads to a lot of otos dying within the first few weeks of being purchased).
That said, I have celestial pearl danios in with one of my bettas (and 3 ADF's in with another) in a 10G with no problems - they are small fish and while mature fish do have flashy red fins, they are very fast little fish and like to hide a lot in the plants and I think that helps.
Last edited by sarahspins; 02-09-2013 at 12:46 AM.