I agree, if you'd like some larger tank mates, why not upgrade to a 10 gallon? The kits for the 10 gallons are pretty cheap at walmart, and many of the kits come with decent lighting (for plants), a nice filter and a heater. Then maybe you could try some platies or something. For now though, how bout a couple Brigdesii snails? they come in all sorts of colors (even purple, I get these at work all the time as "albino" someone at the fish farm is color blind or something!) and get about the size of a golf ball. You would have to feed them differently, but they're still very cool.
what kind of tetras did you try and why didn't you like them? maybe we can give you some better suggestions.
i wish i could go with a larger tank but im in a dorm room setting so a 5 gal hex is about as big as i can go