I had a couple of car stereo speakers sitting in the cabinet in the garage and some other miscellaneous parts relating to those. All I ever used for music in the garage was an old AM/FM radio that worked well, but it didn't allow for using my little portable XM satellite receiver or my iPod or iPhone. So, I ran out and bought a low-end Pioneer 2200 car stereo and a 600-watt computer power supply and BOOM! Semi-instant garage stereo system with XM and iPod capabilities.
[I'll post progress photos here after the weekend when I have a little more time. I just wanted to show some peeps what it looked like completed.]