Besides xCode, here are couple alternate iPhone SDKs. At first glance/installation, Corona makes it dead simple to create flash like games/interactions. It uses a simple LUA scripting language. The Unity 3D for the iPhone is a subset of the larger Unity 3D engine but definitely worth a look if you are building a game or 3d iPhone app.
Find them here:
- Corona http://www.anscamobile.com/corona/
- Unity 3D http://unity3d.com/unity/whats-new/iphone-1.5.1
- Phone Gap: http://phonegap.com/download