Links:

Cycling

CTC - Cycle Touring Club
Wiggle - excellent online bike store
Guide to using GPS for navigation on Audax cycles
The Tour de France

GPS

Bike Route Toaster -- Plan out your cycle routes and download to GPS
Motionbased -- Tool for analysing/sharing your workouts
Sporttracks -- Software to do almost anything with your GPS workouts (superior to Garmin's T.C.)
Open Street Map -- New project with the aim of creating open-source street maps of the world (eventually!)

Electronics/Diy

Make: -- hundreds of crazy creations/hacks
ladyada.net -- source of many interesting projects

Rowing

Pembroke College Boat Club -- My college club
Cambridge '99 Rowing Club -- my current club, if you live in Cambridge, UK then come and row here
Cantabrigian Rowing Club -- my old club - still a great club in Cambridge
ARA -- Amateur Rowing Association
Concept2 -- They make the rowing machines...

Music

Sax on the Web -- Great resource for sax players, particularly the forums
International Music Score Library Project -- Public domain music scores, great for classical scores
PG Music -- Home of the great Band-in-a-Box software

Photography

Fuzzcraft -- several useful tutorials for diy photography projects
Bob Atkins -- he has some great photography reviews on his site
Flickr - where everyone seems to share their photos now