Right now I'm "investigating" buying a new car. And two of my favorite sites to figure out the pricing and availability in the used car market are eBay Motors and AutoTraders. Both sites are great - you can research cars - there's lots of information you can get from must looking. For instance, in AutoTrader, on the results page - if you scroll down to the bottom, you get the following information: Highest Price, Lowest Price, Average Price - for the results. I use this to figure out price range for a specific vehicle.
Now, the new eBay Motors gives you some new pricing tools - you can actually find the range for vehicles that are currently "for sale" and the range for recently "sold" vehicles. And they provide the price right next to the Kelly Blue Book values. Wow, think about this - you have the ability to see what price people are trying to get for their vehicle and on eBay, the price they actually got. Information is power - and now you have two incredible tools for pricing the used vehicle. Watch out Manheim, eBay is providing data to consumers.
Now a personal comment on the pricing sites - Kelly Blue Book, Edmonds, etc. - Kelly Blue Book is completely unrealistic and usually at least 10% high on their estimates and sometimes much higher. Edmonds has a better "market value" approach - but is still only as good as their data. Which will lag behind the data we all have currently at our finger tips through sites like AutoTrader and eBay Motors. Also, do a little research around the web about the Used Car Market - I found a couple research papers that review the general market conditions. Interesting stuff if you like to read research papers. Remember, cars are depreciating assets and it's up to each of us to get the best price possible.