Just over a year ago, Backflip Studios collaborated with Phobic "Team Phobic" Studios to bring DragonVale [Free] to the App Store, and ended up with an incredible hit on their hands. It turns out there are a lot of people out there that like freemium dragon collecting, and they aren't shy about spending money on the IAP as DragonVale has consistently topped the highest grossing charts in iTunes.
Now they're back with a similar take on the freemium collect-em-all formula with Gizmonauts [Free]. Rather than tons and tons of different dragons to collect, take care of, upgrade and breed, Gizmonauts gives you tons and tons of different kinds of robots to collect, take care of, upgrade and... well, I'm not sure how robots breed but you can do that too. Also, enter your little 'bots into online competition against your friends' assortment of robots to see whose is superior.
If you enjoyed DragonVale then I'm fairly certain you'll find a lot to love in Gizmonauts as well. After all, it's free to download and try, and there's a topic in our forums where you can leave your thoughts or questions. Also, robots.