A devkit that allows one to develop iPhone apps in Objective-C, C++ or just plain C with Visual Studio:
Check it out at iOS build env
You can build iPhone apps directly within Visual Studio (2008, 2010, Express).
Pretty neat, it even builds IPA files for your app after a successful compilation. The code works as is on jailbroken devices, for the rest of the planet I believe the final compilation & submission to the App Store has to be done on a Mac. But still, it enables you to develop using a well-known IDE.