Option+F14 or Option+F15 will launch System Preferences and put you into the Displays section, while Option+Lower Volume or Raise Volume or Mute will also launch System Preferences and put you into the Sound section.
[Editor's note: The sound shortcut had been previously mentioned here, but I don't think the same is true for the shortcut for the System Preferences - Display panel. This hint points out that F14/F15 by themselves will control brightness on some (all?) Apple LCD panels.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030211071317504