I've got a refurbished [link|http://z.iwethey.org/forums/render/content/show?contentid=139095|T41] that I'm very happy with. It has a 1.7 GHz Pentium M, I've added 512 MB of RAM, and the battery life is ~ 8 hours with the extended battery and replacing the CD-RW with a dockable battery (it adds about 2 hours).
If you have IBM stock (or know someone who does), you can save a few hundred by buying through their stockholder program.
The iBook and PowerBook are nice machines, but some of the Thinkpads are quite competitive. Decide on your budget first and then see what you can get.
HTH.
Cheers,
Scott.