1fastredsc - before considering a purchase, you should know your measurements, particularly your inseam and the correct length of the bicycle frame's top tube in correlation to your upper-torso length. It can't be stressed enough how an improper-sized bicycle will truly ruin your cycling experience.
After you figure what sized frame will fit your height (especially in the top tube), it helps to have an idea of what the frame is made from. If steel, you'll have a comfortable ride with very nice road feel, but is a bit heavy. Aluminum is lighter, yet unless you're in reasonable shape, might feel harsh if you ride for long periods of time. Carbon fiber gives good response, is lighter than aluminum, has steel-like qualities, but if you're on the heavy side, you might snap the frame.
When you get those two basics down, go :
here.
Lot's of ex-racers post their bicycles for sale for cheap. I liken these classifieds for buying a bicycle to Pelican's "Cars for Sale," as you can really trust the seller.