Well actually I keep them all together in my collection. I know the game preorder/reservation cards come from Walmart or Target, but I keep them with my Farmville, Xbox and other computer game cards. I even keep my Club Penguin cards with my other games cards, not with Disney.
I know there are a lot of cards that only have one or two from a game and new ones crop up all the time.
(Personally I also keep my Game Stop cards with them too. Because hey, it's games to me!)