Yeah, another resource topic. This will also go in my signature ;-)
Some of you may feel that the Audio Portal isn't enough. Some amateur composers may want to compose their own, or just remix some previous game music for their own purposes. Whatever you want to do, you won't find a better topic.
MUSIC //MIDI AND MP3
http://remix.overclocked.org/index.php
http://www.ifni.com/
http://www.sunncity.com/music/
http://billbrownmusic.com/musicmain.htm
http://www.freeplaymusic.com/
http://www.mididb.com/
http://www.gamingw.net/music/
http://www.vgmusic.com/
http://www.soundtempest.net/music.html
http://www.technomidi.com/
http://www.royaltyfreemusic.com/free-music-resources.html
http://www.flashkit.com (Both SFX and Music)
Sound FX
http://www.sounddogs.com/start.asp
http://www.a1freesoundeffects.com/
http://www.grsites.com/sounds/
Next come the specific game music sites:
Nintendo
http://www.megaone.com/dannyone/ssbm_download.html
http://cube.smedia.co.uk/downloads/music.htm
http://www.classicgaming.com/tmk/sounds.shtml
http://www.snesmusic.org/spcsets/
Megaman
http://www.angelfire.com/pq/MegaManMusic/
Sonic
http://www.sonicunited.com/music.php
http://www.planetdreamcast.com/sonic/listen/index.html
Doom
http://www.doomworld.com/music/
Now for those tools to compose new / remix old music/sfx:
http://www.fruityloops.com/
http://www.anvilstudio.com/
http://audacity.sourceforge.net/
http://www.propellerheads.se/products/reason/
http://www.digitalsoundplanet.com/home.html
http://www.sibelius.com
Conversion
http://www.mp3do.com/mp3converter.html
Search these: FindSounds / FindMidis / MidiExplorer / Google
Please note that not all of these are freeware. Also note that most are not royalty-free, so you'll most likely have to give credit if you use the sounds. Check the site for more legal information.
If you have any more, post 'em.