I bought a 2007 Toyota Prius from Carmax in 2010. It has been a joy to drive, gets amazing milage, and went up and over the Great Divide on our 3000+ mile trip from Atlanta to Seattle last January.

Seconding evcelt's Carmax recommendation. I've bought my last two cars there (one in 2001, one in 2010), and I'll probably drive out of my way to buy my next car from them whenever I need to get another one.)