Suggestions on buying a road bike for the city I'm looking to buy a bike with which to get around Atlanta.  My budget is about $500.  

I've seen lots of suggestions for a fixie but those seem relatively difficult.

I plan to ride about 5-10 miles a day.

Any help would be much appreciated!

Update:

I need a bike in order to get around as quickly as possible.  There are few hills, but pot holes and poorly paved roads are a problem.

I do not need racks or fenders.
With this budget, a used bike will get you the best bang for your buck. I was able to find a ten to fifteen year old road bike with good components (Ultegra) and an aluminum frame for around $600. A friend found a twenty to thirty year old road bike with a steel frame and downtube shifters for around $300. Both were in good condition and have high quality components, with the age of the bikes being the main sacrifice. If you're looking for a nice road bike, you can do it with your budget as long as you're willing to go used, but a new bike in this price range will just disappoint you.