some kind of windows mobile device is probably your best bet given what you say you need. if i was buying now I'd be looking at some version of the new HTC Tytn 2 (
HTC: Products: HTC TyTN II ) - not sure which phone companies are selling it as yet.
Your main issue will be with syncing information - unless you're running windows on the Mac, you're probably going to be stuck using 3rd party software - Missing Sync, which is frankly shit. It works, but it's flaky. Be warned!