Come on Valve, this shouldn't be this difficult.
mklink /j "X:\Program Files (x86)\Steam\steamapps\common\NAME OF GAME" "Y:\Games\Steam\Common\NAME OF GAME"
X is the originating drive and Y is the destination drive (the letters will depend on your system of course).
DON'T FORGET to start the game through steam at least once before trying this.
DON'T FORGET to empty the recycling bin after finishing.
*NEW* If you opt in to the Steam beta you can install games to different drives. I haven't tried it, but that's what I'm told.
*NEW (11/26/2012)* If you want to move your entire steam installation (the games and the steam application itself), check out this steam support article: https://support.steampowered.com/kb_a...
NOTE (09/26/2014) I made this video before Steam allowed you to install games to different drives. You can do that now. This video is still useful for moving games that are already installed.
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