Hmmm... get yourself a really good freshwater guide book. That's the best way to figure out what fish you want. Not only will they give you pictures of the fish, but a good book will give compatibility and water cemistry requirements so you know before you get to the LFS what can mix and match. Sometimes LFS employees aren't the most reliable, will bag your Blue Acara, and then you'll be wondering where the heck your neons went the next day (down to the Acara's gut ;D).
But deep-bodied (serpae, bleeding heart, black skirt etc) tetras are good to stick with since you've got tetra conditions already. Gold barbs, cherry barbs, and white clouds are also some small, peaceful schooling fish that will get along with what you have.
There is a whole lot you can do with that tank, and plenty of potential. A good refferance guide is the key *thumbsupsmiley*
~~Colesea