I use good old Palm IIIc and really cannot imagine myself without it (contacts, appointments, to do list, quick notes).
Synchronized with outlook of course.
Tried various fancy Ipaqs but Palm is the best - much faster, doesn't freeze or crash, 3 years and no major issues with syncing with the pc.
PDA/phone combo is not a good choice IMHO...
Sort of difficult to talk on the phone and take notes at the same time
I had good experiences with P900 but it doesn't seem to be as reliable as Palm for the 'organizer' kind of work.