HTC S620
I got one of these last year, which replaced an old iPaq and phone in a package 1/2 the size of either. Not bad at all, though the current version (Windows Mobile 5) doesn't come with a note-taking app, so you need to add one. WM6 will be a free upgrade, and includes Word & Excel, but I'm using OneNote anyway, synced to PC. The keyboard is very usable with a little practice.
If you look at
Expansys, for example, all their current PDAs with keyboards are also phones, so if you don't want that, you prob. need to look at something older (and cheaper). I think there are still folks out there using the Psion Series 5, or HP Jornada 720...