I picked up a cheap leather horizontal pouch on Ebay that has a magnetic flap on it and discovered that the magnet in the flap puts my Droid X in Car Dock mode.
Took me a while to figure out why it was so hot every time I had it in the case for an hour or so.
I didn't pay that much for it and thinking about taking the magnet out of the flap and replacing it with velcro.
I suspect ANY case that has a magnetic closure on it will do this.