Looking around i have seen these:
edit: That's odd the image at
http://www.shirtpocket.co.uk/images/C860_PortLan_m.jpg showed up in the preview. If you can see it let me know, and i'll remove the link above - I'm not advertising for them!
The Sharp Zaurus SL-C860/SL-C3000 they look very capable but are not officially avalaible in the uk, there is a company that will import and convert them though - bit pricey.
Cornish Jack - Was it you who bought my Psion GPS earlier this year on eBay?
Got rid of it as I never used it.
amanoffewwords - I have yet to try a Treo, i'll have to find somewhere that has live ones rather than display dummies.