I'm happy on my Sony Clie PEG-N710C (modified to Palm OS 4, allowing the screen to view 16 bit color). It syncs fine with iSync...I play games on it, and put my school schedule on it.
I use a 4-year old Palm V for addresses, and on trips I'll pack the portable keyboard with it to write and take notes--it's MUCH better than hauling a laptop around, even the small ones. The 12" Powerbook may be light, but since all I need on a trip is the ability to type a little and look up phone numbers, for me you can't beat the Palm Keyboard and a PDA.
I used a Palm iiixe for 2 years when I was going to school and working full time. I needed it to sort out my school work and work projects. It was good for a todo lists for everything I did and keeping track of people and such.
Now that I just work I have no use for it and I broke the digitizer at a bar while drinking too much and forgetting I turned down the contrast.
I'm headed back to school so I'll probably need another organizer of some sort soon. I don't want one integrated into a cell fone because I'm getting rid of the one I have and I don't want another. If there is not an iPod/iCal something soon I might just buy another Palm or PocketPC or something.