I looked at a Uno from their site for a while, but decided I wanted something I could do more with and continued my search - ending in buying something outside of the $500 range.

http://www.bikesdirect.com/products/motobecane/uno.htm

Single-speed is the way to go, imho, for commuting. You get the simplicity of a functional bike without the concerns of dialing in gearing as cables stretch, etc. It also limits the maintenance-able parts of the bike making it easier for you in the long run. Avid 3 brakes are pretty solid, imho and modulate well. You can get wider tires on it, meaning you can absorb most of the harsher road conditions and you still get a drop bar for when you feel like letting the freak flag fly and burning along.

No, it doesn't have an internal hub, nor a rack. But, imho, those things which are considered almost mandatory by many here are outside of the price range on a new bike, imho.

Lots of people will suggest buying second-hand through craigslist.org and the likes. I've talked with my wife, a non-commuting neophyte cyclist, and she wouldn't want me to buy her used because people tend to not take care of their stuff. Especially if they are going to sell it. So its a crap shoot she isn't interested in, and I can assume you're not either.