I used Edmunds (http://www.edmunds.com/) to select the models and years I was interested in. The reviews, reliability rating, MPG, pricing, and specs let me narrow my selections down to the model and years to consider.
I also used Kelly Blue Book (http://www.kbb.com/) to check the prices on specific cars.
Once I decided what models I wanted to look for I used Cars.com (http://www.cars.com/) to locate used ones for sale in my area (and as much as 500 miles away - I could narrow it down as much as I wanted). Many of the sellers have CarFax reports as a link on the listings there so I could check the ownership and history of the vehicles. I could also check reviews of the dealers to evaluate other people's experiences with them.
I ended up finding a 2006 Toyota Prius in excellent condition for $1000-1500 under the Blue Book value at a small dealer three hours drive away. I'm very happy with the car and with my experience with the dealer. We just got back from a long trip in the Prius and it performed flawlessly.
Nearly ten years ago I bought my 1999 GMC Suburban 2500 using the same resources - but back then the CarFax reports we not as accessible - I paid for a limited number of reports to decide what truck I would buy. I still have that Surburban and am still very happy with it, too.