I fail to understand why people insist on ruining a slick content delivery tablet (iPad) with desktop applications. If you want to to do heavy duty content creation grab a MacPro or MacBook Pro. Honestly, I can't believe there are people who think they can run something like iMovie and edit video files on an iPad. Apparently, a lot of people just fundamentally do not understand what the iPad is (or isn't).
As far as applications go, I don't have any ideas that haven't been mentioned. I would, however, love sone kind of viewer application for my Sibelius scores that would allow for a limited amount of editing (transposition, etc.). I'd also love a viewer for my Pyware 3d files that would enable them to animate within the application.
I know I can accomplish some of these things with PDFs and video files, but it would be wonderful to eliminate the middle-man, so to speak.