OMoS, your best bet right now is to dig through Ham Salad's Cars folder at Flikr (at least for what has already been released), decide what you want to get and then find out how each of those cars was released. The biggest problem with making any sort of "simple" guide to Cars is just the number of ways these things are released (singles, two-packs, three-packs, four-packs, five-packs, thirty-six-packs, etc).
http://www.flickr.com/photos/hamsalad/s ... 285689434/
The Drive-In Gallery is nice for what it is (if it's working, that is) but it's a bit much to wade through for quick reference. Take5aDay.com
is also a great reference site with lots of good info on what's on the way, but it takes some digging through some rather silly and pointless posts to get to the good stuff.