The iPhone Development On Windows Options

1) Flash CS5 – At the moment is probably the most complete solution.  The packager for iOS allows you to compile apps on the windows platform.  If you’ve been using flash you can rejoice in Apple’s latest policy, it performs well, but don’t expect highest performance games, and Papervision to run in here.  No mac required.

2) Airplay SDK – The airplay SDK allows you to create games, and sign your app on Windows PC’s.  I have not tested this solution, but apparently many apps have been created this way.Both these solutions can compile to code that is native to the iPhone right on your windows PC and many apps available in the app store have been created using them.

3) Unity 3D – Game development engine and editor that utilizes Boo and C# and the editor works on both Windows and Mac.
4) Stonetrip S3D – Game develop engine and editor utilizing LUA, the editor runs within Windows.
These game engines allow you to develop your apps on Windows, but you’ll need a Mac to test/compile.

5) Appcelerator Titanium – This is a good solution, and has a very popular and vibrant community.  Apps are limited in performance because while they can be compiled as native apps and sent into the app store they are html/javascript based.

6) Genuitec MobiOne – This is an interface designer that uses the Phonegap framework to deliver native functionality.  It only runs on windows.  HTML/Javascript based.
These solutions allow you to create apps using web technologies (HTML/CSS/Javascript) and then run them through an Objective-C framework that responds to actions within a UIWebView, thus allowing you to access native functionality on the iPhone.  These frameworks are free.
7)Dragonfire SDK – An interesting option that allows you to develop apps using their SDK on windows.  Then you send them your uncompiled source which they compile and you download the compiled iOS application file.  I’ve been asked if this means they get a copy of your uncompiled source code.. I couldn’t tell you that, I just know that you have to upload your code for compiliation to their website — but hey you wanted to develop iPhone apps on Windows.  Overall this is a wrapper, I like the syntax and it’s pretty popular so I’ll mention it.
There are a couple of other solutions that were either in testing, required payment without any form of trial (or in some cases even screenshots), or just aren’t out yet many of them seemingly lesser versions of the Dragonfire SDK that enable iPhone development on Windows by compiling your source code for you..  Creation tools like Titanium have become a dime a dozen really.. Airplay SDK is probably the most advanced “iOS SDK on Windows” available free at this stage.