If wireless is important to you then it is Blackberry all the way...the thing has changed my life...really.
If you can, wait til the fall when RIM is rumoured to be launching a colour version possibly with phone capabilities.
In Europe the are launching a GSM version of the 957 which does voice.
If all you want is a laptop synch of your calendar, contacts...etc...then get a cheap Palm of Visor.
If you want to do MS Office type stuff, MP3s, maps....get a Windows CE device.
If you aren't technical get a Windows CE device (such as a Casio).
This is some of the stuff I consult on at companies...picking the correct technology. If you are more specific about your needs I can list you the exact device to best suit your needs.
Dorian