Travel Concept Solutions makers of PowerTrans translators and phrasebooks. Excellent translation software!
Foundation Systems makers of Mapper and a lot more.
Currency Updater updates daily(?) the currency exchange rates in the time zones application. (at last check the site was down)

The essential sites:

info-newt and the FAQ for the Newton Community .
The Son of Ultimate Newton more links than you can shake a stylus at.
NewtWho? ditto.
DNUG: Newton Versions like version tracker, just smaller.
Planet Newton not as up to date as the others, but still a great source.
the Newton Info Library where all the Apple TIL articles went.
Masa Newton for Japanese speakers and hobbyists.
Newton Padawan for newbies (and Star Wars fans).

Software archives

Newton software at Excite
NewtonUser
The Newton Source - The essential Apple Newton reference!
The Newton Cage European Mirror
Newton Intelligence Hotline Server (huge archive)

Newton software authors

Standalone Software
Catamount Software
MISNIC
Revelar: Revelar Connection Utility and Notable
DejaVu Software
Newton's Prism
Steve Weyer's Newton Releases
Peter's Newton Web Page books and maps.

Miscellaneous

Discussion Threads at Smaller.com
Newton WebRing
Newton on Govmail
DSpires Newton Links
The Newton Underground
Newted Community webspace and email for Newton users.
The Hong Kong Newton User Group
Project Newtonberg
Brett's ebay Page a collection of Newton eBay auctions.