The spectacular signal processor. 100 programs, 21 effect chains in the basic configuration. Expandable with several ROM cards with new effects and chains. The cards can also be loaded with a MIDI cable.
Famous Korg A3 users: The Edge, Steve Howe, Eliot Easton.
Not so famous: me.
Check out the Korg A Series usergroup at http://www.korgaseries.org.