I can see crosswords and similar games taking off for people who use their kindle to read newspapers. It's one of the major (to some people) sections missing from the kindle versions right now.

I think we could also see apps that use the kindle as a tool for producing content, not just consuming it. Writing blog posts, kindle twitter apps, etc. The keyboard leaves something to be desired, but I could still see this type of thing being popular.

Basically, the successful apps won't be competing with what you see on the iphone, they'll be unique to the device.