Oh, man. So many I could mention, but are a few of my favourites.
Red Threat - A splendid source of new electronic musics that I probably wouldn't find anywhere else.
My Blog Too - Contains a lot of interesting hard-to-find oddities. If you're looking for that elusive Ringo Starr live bootleg, it might just be here. It does seem to have gone a bit Duffy crazy latterly.
Indie Flames - from Alone At 3am to YMCK, it's all here. A great source for music you didn't realise you liked.
7 and 12 inch Massacre - All those CD singles you wish you'd picked up when you were in Our Price in the 1990s.
Burning The Ground - 1980s and 1990s remixes galore. Includes an essential French version of PSBs' New York City Boy (renamed, of course, Paris City Boy).
Secret Music Box - All codes of electronica catered for.
Twisted Perceptions - Japanese Psychedelic Music? Peruvian Underground '64-74? Turkish Beat, Psych and Garage? Oh yes.
Different Is Dangerous - Unofficial remixes, mash-ups, and collections of pop classics. Brilliant stuff.
If you've got any taste in music at all, there's a whole week's worth of listening pleasure in those links just up there.