Another note for the guitarists: If you have an ipad, ipod, iphone, you can get an application for it called Guitarist Reference. The freebie version at iTunes is fine, and the fully-featured HD version is $4.99, and so far, I've found it most useful for those moments when I need a quick reference and am away from my shelf of musical reference books.
I tried the freebie version, liked it, then upgraded.
There are all kinds of instructions you can use, ranging from scales and chords, to arpeggios, a reverse chord finder, notes on the fretboard, a quiz, and alternate tunings. You can hear notes, played by tapping them, all like that.
Gets four stars, and probably would have gotten five, though people gripe because there is no landscape view. (And I just love reviews where somebody says, "very dissapointing." [sic]. If Jesus came back tomorrow in a blaze of heavenly glory, you can book it there'd be somebody who wouldn't like how He did it, who'd give Him One Star, and probably misspell His name ...)