Check out this link to Winding Road
Winding Road contacted me earlier this week. They actually found me while looking for another company with a similar name (and I thought I was just so clever! (not!!!)). Seeing as they are based in Ann Arbor (as our Car and Driver and Autoweek ) they stopped by for a chat and a test ride.
I say "mainstream" in quotes. They have a great pedigree in their founder - but they're Internet only and they're relatively new.