Any ideas what you like?
Livebearers are a good place to start. Guppies, Molly's, Platys, Swordtails to name but a few. Keep either the males if you don't wan't fry. But the fish breeding is half the fun of fishkeeping.
A tank should have a few 'dither' fish. Most tetras are good for a start. They need to be in a shoal. Maybe 5 to 10. Neon tetras are the classic tropical fish and still look great even though nearly everyone's got them.
Cichlids are a great type of fish, angels are the classic tropical fish too, but they will make a meal of small fish like neon tetras.
This list is not exaustive by any means and i'm sure more people will have suggestions.
My best bit of advice, what i did. Research, research, and research some more. Read books, get fishkeeping magazines, visit fish shops and see what they have and talk to the staff. The shops that have time to talk and really seem enthusiastic about the fish are the places to go.