Links to other sites (in no particular order):
www.hp41.org
www.hp42s.com
JFG's Page
Eric's Page (Nonpareil)
Valentin Albillo's Page
Free42
Massimo's Page
www.hpmuseum.org
www.hpcc.org
www.rskey.org
www.datamath.org
www.hpcalc.org
www.hp41.net (in french)