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)