Adobe makes a Windows Mobile PDF reader that comes on the Fuze stock ROM if I remember correctly.
I guess I'll bring up what I just used today so far.
I use some Citrix server apps where I can remotely access my servers with full live screenshots at 640x480 resolution and also be able to easily transfer files wherever I am.
I like that I don't have to buy an app just to listen to an online radio audio stream that uses Windows Media or Shoutcast. I've been told that the iPhone does not fully support all Window Media streams yet.
I love that the Fuze can double as a wireless router and feed any of my wireless cards an internet connection in a pinch.
Garmin has great GPS software that looks like their GPS units and works great on the Fuze.
And I really like to be able to copy and paste