I agree with Drew. Bluefin killies are great little fish, and can often be had for free. Keep an eye on the ghost shrimp tank at your LFS and watch for straw-colored little fish with two black stripes. Only males have bright fins and they usually aren't colored up in the shrimp tanks.
Pygmy sunnies are a little harder to get a hold of, but still not bad. Several online retailers sell them, including Zimmerman's in Ohio and Sach's in Florida.
I've kept pygmy sunnies, bluefin killies, and ghost shrimp together in the same tank with no issues.