I have had my Tetras for about 3 years now. They are easy to take care of, and very hardy. They also come in a wide variety of colors, shapes, and sub-breeds. My personal favorites are the strawberry, blueberry, headlight-taillight, and zebra tetras. They are friendly fish that will get along with your tank.
Mollies and Danios are also pretty easy fish that come in a wide variety. They get along with all of the other tropical fish as well. I like the sunrise mollies, lyre tail, and sword fin varieties. Bottom dwellers and algae suckers can also be very easy, and help keep your tank at its best. Chinese algae suckers, catfish, angelicus, and cory cats are all very easy and hardy fish.
Between these fish alone you could build a beautiful tank. These are just a few examples of fish that are friendly and easy to take care of. But ask the person at the pet store, they can help you find out what fish is right for you. I keep my fish tank at 74-76 degrees Fahrenheit, and an approximate ph level of 7.2.