We just picked up 2 Evenflow Discovery seats with 2 extra bases for the granddaughters. The car seat portion snaps out of the base and can be used in the other vehicle which will allready have a set of bases in it.
Go to www.evenflo.com
to check them out. I liked the base idea because of the ease of just transfering seats and not having to strap the car seats in everytime you switch vehicles. Plus in our situation when the daughter drops them off in the car seats as carriers, we have a set of bases to safely transport them.
edit, yes her car is a GP and ours, well , you know.