I use an older Jornada 540 with 32MB internal RAM and running Windows CE.
On the plus side, it is a very sturdy piece of kit and mine has survived quite a few drops. It also has a very good metal cover which gives added protection. The memory is expandable with inexpensive CF cards and you can still find bits and pieces for it on ebay.
I have successfully tested Ozi explorer and TomTom software with a Rikalene wired GPS but be advised that newer versions of TOMTOM will not work with windows CE... it's important to find the correct versions. I also use a Targa portable keyboard which, although full sized when deployed, folds up very small (not much bigger than the PDA.) I had no problem getting batteries, cables, screen protectors, chargers , cradles and various other accessories, mostly on eBay.
On the down side, It is not waterproof , although you can get waterproof pouches for it, Software availability is very limited although Navigator V2 pops up on eBay now and again. TomTom coverage outside UK is verylimited and I found Route finder Europe rather limited with no ability to zoom into the maps. City Navigator is good however although you have to load each city map individually. Ozi explorer worked well although I have not taken the time to get any decent maps yet. I have not tried fugawi yet but there may be a Win CE version available ( I'm still looking). There is also a camera for it which plugs into the CF card slot. They sometimes pop up on eBay.
There is lots of old Jornada programs floating about on the ptp network ( Emule etc) but pretend I never said that!
All in all, my Jornada is a very usefull piece of kit but it is quite dated and does not do everything I would like it to do. Certainly can't replace a Laptop but is small enough to keep in a top pocket.
Type Jornada into the ebay search box... you will see plenty of stuff.
If you never make mistakes, you ain't trying..