LARTC - The Linux Advanced Routing & Traffic Control Howto
This should be your first stop if you're considering anything more than rudimentary networking.
Linux IMQ - The Linux Intermediate Queueing Device
The IMQ allows for shaping/throttling of ingress network traffic.
Offensive Security - Penetration Testing Courses
If you're serious about entering the field of penetration testing, muts and his team of security professionals provide an excellent series of practical online courses for the networking professional. I took the "Offensive Security 101" course in the autumn of 2008 and use the newly acquired skillset every working day.
G1SLE.com - Richard Drabble
Richard is a colleague, friend and keeper of the GB3EE and GB3RB amateur repeaters. He has developed some interesting products, including a feature-rich repeater logic board and DTMF-operated voice switch.
The Listener's Guide - Bob Ellis, G8YQL
Entering its seventeenth year of publication in 2009, The Listener's Guide continues to provide an exhilarating insight into the field of Shortwave Radio. Whether you're taking your first steps into the world of Sideband, Sunpots & "Sferics" or you're a full-bearded radio guru, Bob's informative and humorous musings will have something for you.
Just 30 - Web Design
Like the design of this site? Just 30 offer a friendly service from their base in Sawmills, Derbyshire.
Just Plain Stupid
Disgruntled Goat - Harry Sheppard
Perhaps adding Harry's site to this section is unjustified - DG has an interesting (if apparently random) selection of content, ranging from how to calculate the MTBF of your shiny, new RAID array through to effective distruction of old computers. See if you can spot me killing the BBC Micro with a ride-on mower!