Mac OS X – Spotlight hotkey is, by default, 
+ space bar (apple/command + space bar).
Because I use Quicksilver, I changed the spotlight hotkey to CONTROL + SPACE, and then the Quicksilver to COMMAND + SPACE.
If you’re on a laptop and you don’t use Quicksilver much, I would just leave it at COMMAND + SPACE because the control key is hard to press with the Fn key right next to the control key (a pet peeve of mine).
