Originally Posted by: magicninjaBackingtracks? Never heard of 'em.

Sometimes they're called Karaoke, although that term is usually reserved for singers. Same thing though... backing tracks that have been redone by other musicians to come close to the originals.
If you have usenet, you can get a lot of real instrumental versions from places like alt.binaries.mp3.bootleg etc...
I got a ton of Queen, Van Halen, ELO stuff where somebody's gone back into the studio, removed the vocals and done an instrumental version.
Lot's of Beatles stuff too. There's probably more recent stuff but you'd have to request it & see what happens.

You can also use MIDI files for backup. A lot of them are crap but occasionally you'll find a MIDI version of a tune that's actually better than the original.
Again.. usenet's your best bet. alt.binaries.midi etc..
Otherwise you'll have to buy them cause of copyright issues.

I'm sure by now somebody has come up with CD's you can buy specifically aimed at guitar players with backing tracks on the too. Just check the various music publishers & stores.

Oh yeah... you can also get Band-In-A-Box. Kinda cheesy sounding but good for practice.