The links below were taken mostly from a fark.com forum topic. After the description I've noted the player(s) needed. If you have a station you'd like me to add, drop me a line.
Meta sites
Accuradio - numerous stations/formats - requires java
Warp Radio - directory of online stations - windows media
Shoutcast - directory of online stations - winamp
Live365 - directory of online stations - requires download
LaunchCAST - numerous stations/formats - requires free registration
Iceberg radio - numerous stations/formats - requires free registration
RadioIo - numerous stations/formats - requires free registration
Jazz
Jazz91 - Jazz91 SF Bay area - straight jazz - listener-supported - wmp/realplayer/winamp/itunes/quicktime
KPLU - "NPR news and all that jazz" - windows media player/realplayer
WNCW - North Carolina - bluegrass/jazz/folk - windows media player/mp3 player
KBON - cajun - mp3 player
Rock
WXRT - Chicago commercial rock - requires download
The Edge 103.9 Phoenix Arizona - modern rock - windows media player/realaudio/quicktime
Egg Radio - eclectic mix of alternative/rock/ska - mp3 player
Indie 103.1 - los angeles indie radio - windows media player - plays in popup
Rock Chicks Radio - all female artists - winamp/windows media player/realplayer
9412 - the rock station - winamp/windows media player/realplayer
91x - has love line - require free registration
WOXY - 97X the future of rock and roll - modern rock - windows media player/mp3
Radio Paradise - eclectic rock - mp3 player/windows media/realplayer
Wazee - modern rock - mp3 player/windows media/realplayer
106.9 the Point - Houston - 70s/80s/90s - download required
3WK - underground alternative - indie rock/classic rock - windows media/realplayer/winamp/ogg vorbis
NUGS - grateful dead/phish/string cheese incident - mp3 player
Electronica/techno
Soma FM - underground/electronic/ambient - seven different themed streams - mp3 player
Spank Radio - indie/emo/spacerock/electro-clash/dream-pop/fusion - mp3 player
DI FM - Digitally Imported - trance/techno - mp3 player/window media
Frisky Radio - house/progressive/tech/experimental
Monkey Radio - trip-hop/acid jazz/downtempo/abstrakt beats - mp3 player
Bassdrive - drum n' bass - mp3 player
Blue Mars - music for the space traveller - trippy/ambient - mp3 player
Epiphany Radio - ambient/trippy/jazzy/chill - mp3 player
Lounge Radio - fresh beatz/downtempo/new jazz - winamp/realplayer/windows media/quicktime
Proton Radio - house/techno - mp3 player/windows media player
Digital Gunfire - industrial/ebm/synthpop/darkwave/gothic - mp3 player
Funk/R&B/Hip-Hop
KUBE 93 - seattle hit music - windows media player
WeFunk Radio - deep funk/underground hip-hop/rare grooves - mp3 player
HURRadio - Heads Up Raw Radio - underground hip hop - mp3 player
Breakpirates - oldskool breakbeats - mp3 player/realplayer
Variety
KCRW - public radio - "innovative and eclectic music" - windows media player/realplayer/mp3 player
BBC Radio 6 - BBC radio 6 music - windows media player/realplayer
KEXP - university of washington - rock/hip-hop/electronic/country/blues - windows media player/realplayer/mp3 player
WFUV - fordham university public radio - windows media/mp3 player
WRSU - Rutgers Radio - realplayer
CKUA - University of Alberta - windows media player
Other
Radio Rivendell - Soundtrack music for fantasy roleplaying games - winamp/windows media player/other
Gaming FM - gaming music - classic console/modern console/pc - mp3 player
The Ticket - sports - windows media player
WQXR - classical station of the New York Times - radio@AOL/radio@netscape - requires download
Air America Radio - progressive talk radio - windows media player/realplayer
Solo Piano Radio - Whisperings solo piano radio - requires live365 player
Hawaiian 105 - KINE Oahu - hawaiian music - download required
ACB Radio - radio for the blind - featuring the Treasure Trove old-time radio - mp3 player/winamp/realplyer