Well VGMUSIC.com is a great site, but its powered by MIDI's, which are only as good as your sound cards MIDI bank, and most aren't very good at all, unless you pay for a better, more expensive set.
Though these files tend to be small since they only carry MIDI data and no sound, there nothing like the originals.
I use MOD files (or their equivilents). These represent the originals completly.
Almost half my hard drive are MOD filled, with game music, and from music composers dabbling in the field.
PLUGINS FOR WINAMP AND STANDALONE PLAYERS:
MOD stands for Module, and these sound formats need a player to play them.
Winamp for instance can play them very well once you install a few plugins from here:
So if you have Winamp, check out some of those plugins for the different consoles.
CONSOLES AND THEIR MOD FORMATS:
Each console you see will use a different MOD style.
PC MODS come in a range of formats, like XM, S3M, etc
Then theres Amiga, which originally started the format with MOD.
Megadrive/Genesis MODS have the extension .GYM (Because they are ripped from Genecyst, the emulator)
Snes has the format SPC.
I for one have all the score from Super Mario Allstars on SPC files playable by Winamp, which includes Mario 1, to Mario 3, and some secret level music too ripped straight from the game, so they sound completely like the original.
I also, if anyones interested, have the GYM files for all the Sonic games
HOW MODS WORK:
Plus, they don't work the same way as MP3's. MODS store the sounds used within the music in the file itself, and as played, the sounds are picked up from the memory and played in order.
So Winamps plugin is basically going down a whole list while a piece of music is playing (how it was originally made) of checking for the bank number/the sound, the key pressed, and the velocity it was pressed, and also the effects to place on the sound (rather like MIDI, but the sounds are built in, but they work almost the same way).
This is of course dependant on your sound card, and how many sounds it can actually play seemlessly, but also depends on your CPU since it has to do all this in the background, with processing.
MODS of good quality formats can play about 40 channels in one go, but console music only tends to have 4 to 10 depending.
On a final note, its very easy to find MOD and its equivilent music on websites. You may have encountered it before, but just didn't know how to play it
I hope this helps.
If you have MSN i would kindly give you whats neccessary, and also send you the score for Mario too if you wished.