I would recommend a few different solutions, depending on your level of comfort.
For the expert...
Performics, they do Toyota, Chrysler and Lexus SEM as well as an increasing number of dealers. This is a good solution for dealers that are ready to start driving strategy.
Omniture, a lot of different tools there for an advanced user. But, as Jeff mentioned it's fairly pricey. Best Buy is in the process of migrating to this right now.
For the average dealer...
Cuneo, we've got a great tool with full on-demand reporting and industry leading expertise with A/B and multivariate testing capabilities
Dealer.com, they've got great tools with an easy-to-use interface that appears to work great within a Dealer.com website
A few notes (for the beginners)...
In general, you're looking at a 15-20% commission rate taken out of your budgets for a managed solution. If you're paying more than that it's probably time to look for a new provider. Even at those numbers, companies with dedicated staff or automated tools are always going to outperform individuals that have limited time split between SEM and the myriad of other dealership responsibilities.
Also, ask what happens to the click fraud charges. Occasionally, companies will pocket that instead of putting it back into your budgets.
