ZumoDrive takes things a step further than typical cloud storage with their iPhone application. Since I have already gone through ZumoDrive in detail tonight I'll just throw out the highlights of their iPhone app.
Features
Music is organized by Artist, Album etc so it is easily browsable. If 16gb isn't enough storage space for you just load your tunes up onto your ZumoDrive and for playing where ever you have your iPhone. Music plays over 3g just fine and you can even have some album art. .mp4 support needs to be added in but should be there soon.
The Pictures feature works much like their snazzy web interface automatically creating nice little slideshows to view from the iPhone.
You can view documents straight from you iPhone. Most all common file extensions work.
The interface is easy to use and self-explanatory (as show in the slideshow above).
What Needs to be Improved
AAC support.
Landscape mode for pictures and documents.
Not much else. The current app