Have been reading up on this, and the M-Audio iControl has been mentioned as the only control surface with native GarageBand compatibility, but it's no longer available.
However Korg offers a GarageBand plug-in for use with its nanoKontrol2: http://www.korg.com/uploads/Support/nanoKONTROL2_PlugIn_GarageBandLogic_E1_634479713702770000.pdf
But it seems that at least one person had issues with this and GarageBand 11: https://discussions.apple.com/thread/2630372?start=0&tstart=0
So is anyone here using a control surface with GarageBand 11?
However Korg offers a GarageBand plug-in for use with its nanoKontrol2: http://www.korg.com/uploads/Support/nanoKONTROL2_PlugIn_GarageBandLogic_E1_634479713702770000.pdf
But it seems that at least one person had issues with this and GarageBand 11: https://discussions.apple.com/thread/2630372?start=0&tstart=0
So is anyone here using a control surface with GarageBand 11?