Just a controller - no sounds needed?
In theatre world (where I occasionally play) - I see Oberheims and Kurzweils driving VSTs. I don't own either (too heavy for me) but I did consider this for running my VST rig (laptop + Kore).
http://www.soundonsound.com/sos/nov9...s/oberheim.htm
They weight a lot but reliability must be good or they wouldn't use them for touring show.
BTW: For my laptop+Kore live rig I went for a used 76 key Roland A-33 on EBay - very light, fine for piano organ and synth (for me anyway - though no sliders for organ VSTs) - can run on batteries (for ages) if needed - cost £80 + £30 postage with a case I think. They're not expensive second hand. If you see one it's a cheap way to dip your toe into the world of VSTs. It's MIDI only - you'll need someway to plug it into your Mac.
That Kurzweil Elmwood is championing would be my choice if money really isn't a factor. You may not always want to set up your computer to play - just fire it up and stick in your headphones.