Tell us a bit about who you are and the people you reach
Everyone in the app store. Probably skewed slightly towards people 18+ (the 9-5 crowd).
It must prominently feature a 3D umbrella. It must look really really really well-designed. (Our interface is really well-designed.)
The icon must come in a 57x57 version and a 512x512 version (I would strongly prefer a vector illustration but this will not affect your chances). Optimize for the 57x57 version--- the 512x512 version is not as important. Your art must not contain or depend on the iPhone icon "shine".
Fair warning: I've seen most of the clip-art umbrellas out there and don't care for them. In general I'm looking for something more detailed and more 3D.
If for some reason you lack creative vision, lately I've been partial to the CandyBar icon (http://www.panic.com/candybar/), though not necessarily the color scheme. I don't want to see a bunch of ripoffs of this, though.