Hey! I have a great little idea for you!
Make an app that:
1) Opens up a song in the music library.
2) Lets you select a few seconds of the music, e.g. A line in the chorus, etc.
3) Fade in/out on the clip.
Sorry... That was naughty of me... Of course you can't do that because you don't have file access to the media library in iOS. You would simply bang your head against the wall in frustration as things are locked down to insane levels.
How about a custom browser that lets you surf Apple Hate sites?
While that would take you around about 10 minutes in Visual Studio, you'll quickly find that it takes a day or more in Xcode...
Man... I gotta come up with better ideas...
Ok, how about this...
Nah... You'd just pull your hair out again...
Ok! I've got it!
A comprehensive hello world app that demonstrates multiple screens that maintain state with different widgets/controls on the various pages, does a few nifty things, like animate Cody or something, and links back to the tutorial page on DC~!
DC iOS Hello World~!
It would let you explore things and write up an article on it all.
In any event, good luck.
Oh, and you might want to look at MonoTouch as you can use C# instead of Objective-C, which may lead to less hair loss. (And you're not forced into Xcode... where everything takes 3x as long... on a good day...)