Tom's Harware Guide provides lots of low level info.

Bakewell Computers sell "surplus" s/w if you dont need the latest version.

Download.com are an online S/W source.

KryoTech supply the ultimate in high speed PCs.

PC Magazine , SW downloads

Jochen's Various Psion links.

PSION IR Link Programs

More commercial : Widget , Psion , Psion Monthly

More series 5 stuff at 3lib