10.7: Unbind your Spaces Key
Your 10.6 Spaces key gets redirected to Mission Control automatically, but there is no option in System Prefs to unbind that key or cleanly reassign it.
To do that, you'll need to edit your symbolichotkeys plist:
Log out/in and your key should be free. [crarko adds: I haven't tested this one. The com.apple.symbolichotkeys.plist file is in ~/Library, and you may wish to back it up (Time Machine or otherwise) before making any changes.]
defaults write com.apple.symbolichotkeys AppleSymbolicHotKeys -dict-add 75 "{enabled = 0; value = { parameters = (65535, 96, 0); type = 'standard'; }; }" defaults write com.apple.symbolichotkeys AppleSymbolicHotKeys -dict-add 76 "{enabled = 0; value = { parameters = (65535, 96, 131072); type = 'standard'; }; }"
Source: http://feeds.macosxhints.com/click.phdo?i=308bf19ad9ffc15a8b576defa14bab9b