Apple GarageBand '09 - Manual (Page 119)

Appendix A Keyboard Shortcuts 119
Open Command-O
Close Command-W
Save Command-S
Save As Command-Shift-S
Application menu functions
Show GarageBand Preferences Command-comma (,)
Hide GarageBand Command-H
Hide other applications Command-Option-H
Quit GarageBand Command-Q
Help menu functions
GarageBand Help Command-question mark (?)
Action Shortcut