Here are some links I find interesting.
Astronomy and Physics
3D Starmaps A site full of 3D starmaps and sky catalogues
Fusion - Tokamak research in Europe
Institute of Physics - Professional association of physicists in the UK
Jodrell Bank - The Jodrell Bank Radio Observatory based in Cheshire, England
JPL homepage - Information and news on many past, present and proposed NASA projects
NED - The NASA Extragalactic object Database
PPARC - Funds particle physics and astronomy research in the UK
Stuart's homepage, with more links to astronomy sites than you can shake a mirror at!