Both of my keyboards have now arrived.
IBM Space Saver II keyboard (using generic Synaptics driver & IBM trackpoint driver) was only $45 on ebay.
EnduraPro (default driver)
Endurapro's mechanical keys are prefereable to the space saver's membrane keys, but they're both far better than the current Ultranav/Thinkpad flimsy keys that are impossible to replace.
The EnduraPro's pointing stick is much better than I hoped, it's nearly on-par with trackpoint. The downside is that there are no custom drivers for it, so you're stuck with the default sensitivity that your mouse uses (which for me was high, just how I like it). The Space Saver II is a real trackpoint so I can use synaptics drivers with it, and adjust the sensitivity independent of my mouse. The Space Saver II also has the middle-button, which gives it a big edge over endurapro's 2 button setup.
They are both great trackpoint keyboards. Luckily I don't have to choose between them, since I use two computers
If I had to choose though, here's how I'd do it:
Surfing, Reading, Navigating - Space Saver II
Writing - EnduraPro
I'm much happier with these keyboards than I was with the Ultranav keyboard, which is quite a feat since I loved my ultranav.