Via MobileMe for Calendar, contacts, & emails. Other things no.

Not until they do more updates. Maybe in iPhone software 4.0

Air Sharing can do this (search in the App Store). You can transfer files (almost any) to your iPhone with a wireless network and there’s no internet required to do this. The only think I don’t like about it is that you don’t have the option (yet) to save music, videos, or photos to your iPhone and they can only be viewed through the app.

Lurve for @TheCreative; I’ll try that out.

If you use Google’s email and calendar, then you should check this out: http://www.google.com/mobile/products/sync.html#p=default

I actually just started using @aidje suggest of syncing my google calendar with my iPhone. Works really well and it pushs new info.