I was also going to suggest Kelly Blue Book.com but also another website (which the name escapes me now!!!) This particular website will list how many owners, who the owners were & if the car had been involved in any accidents. Can someone help me here???? Oh...is it Carfax.com? Anyway, for a $20 fee we found out that our van was formerly owned by a "company" & not only were the miles extremely low but it had never been in any accident. I should also mention the sticker price on our van was a tad over $42,000 (it has all the bells & whistles) & we purchased it 1.5 years old for $17,500. We've now had it for a little over 2 years & no problems.
One more thing, ask the dealer if he'll supply you with the carfax.com sheet (another dealer offered it to us but we decided against that vehicle). The worst they can do is say "no" but if they want the sale, they will furnish it to you at no charge.
Another little fact I learned recently is that you don't have to purchase the extended warranty from your dealership. I think you can even go through Costco to buy it at a considerable savings. Check it out!