I just got a 'new' 2003 Cannondale R800 for under $700US. Shimano 105 and a CAAD5 frame - I think it's a good start. This was my first road bike and I didn't want to blow too much money on it, in case I didn't enjoy it as much as I thought.

I'm all for buying an older bike if you can verify the quality of it before you buy.