I like bluefin killies a lot, but they stay pretty small - only 1.5" max. I've found golden topminnows a lot, and both sexes are quite pretty - the males get pretty spectacular! They max out at 3" - perfect for a 30 (start with small ones, they acclimate better). Seminole killifish are pretty common, get a bit larger, but will do well also. Dollars are present in our area, but are really hard to find. I've had much better luck picking up the bluespots, and they are also much less aggressive - makes for a better community tank.
When your tank is ready, PM me. I know some good spots for stuff.