Awesome! I grew up with freshwater fish.
My favorites were the mollies, especially golden ones.
Remember, your initial set of fish are probably going to die, so don't get too attached, and don't buy expensive fish at first. Guppies are a good start. Your second and third batch might die too. Chemical levels take a while to balance out. I'm sure you already have a test kit and the right additives to help out.
I'd recommend, along with the pretty fish, you get an algae eater or two, and a catfish. They'll keep the bottom of the tank clean. Once your levels are ok and your fish stop dying, you may want to invest in a plecostemous (sp?) fish, which keeps the sides of the tank clean too. These grow to a size to accomodate your tank, come in cool skin patterns, and have personalities.
Avoid - tiger barbs and anything shark-looking. They tend to have bully personalities and gang up on other fish.
Awesome project! Enjoy!