Does anyone know of another good game SDK/Engine for the ipad or iphone other than CORONA?
The above answers are great possibilities. I highly recommend unity as it just came out with its newest release that offers a gajillion wonderful features like batch rendering, beast lighting, etc. Its also ridiculously easy to program (im surprised there isn't a 'make this game for me' button in it). The price is worth it. By clicking a button, you can publish your game to pc, Mac, web, iPhone, iPad, xbox, wii, ps3, or android, depending on whether you purchased the license for each. It' bloody magic. Keep in mind that you need to buy the unity pro license before you buy the iOS license. One does not work without the other. It'll be a total of around 3 grand USD, but again totally worth it. Community is rad and helpful too.
If you're going the free route and have some coding chops, I'd run with openFrameworks. It's a c++ wrapper of the iphone sdk and has a very low learning curve. OpenFrameworks was created for artists who wanted to make interactive installations and art games but couldn't get really deep into objective c. Check out zach gage's work (stfj). He made bit pilot, unify, synthpond, and sonic wire sculptor all in open frameworks. He's also releasing his best yet very soon for the iPad. My own company is using oF (openFrameworks) for it's new game releasing this coming Saturday. Try it out. I guarantee you'll find something you love about it.
Unity3D - very cheap compared to comparable environments. Now adopted by EA, Sony and all sorts of people.