Handheld Manufacturers

Handspring - Soulfrost owns one.
IBM - Nice Palm clones.
Palm - The Original Palm OS manufacturer.
Sony - Small and sexy handheld.
TRG - Built in Compact Flash support.

Software

Fictionwise - Tons of ebooks.
Palmgear - Hardware and software.
Palmtracker - Always up-to-date.
Peanutpress - Great source of ebooks.

Other Useful Sites

Pentopia - Makers of the Chameleon stylus.
Memplug - Springboard Smart Media Adaptor.
Rhinoskin - Great cases for handhelds.
Vaja - Beautiful leather cases for handhelds.
Visor Central - The Visor site Handspring goes to.
Visor Village - Great Visor site.