Of recent television animation, I was regularly surprised by the list of guest voices on Hercules. Not only did the regular cast list include Tate Donovan, Sandra Bernhard, French Stewart, James Woods and Robert Stack (as Bob, the Narrator), joining in on the fun were such voices as Alice Ghostley, Mandy Patinkin, Jane Curtin, David Hyde Pierce, Heather Locklear, William Shatner, Idina Menzel, Jodi Benson, Merv Griffin (as Merv, the Griffin), Eric Idle, Jonathan Freeman, Reba McIntire, Carl Reiner, and yes, Robert Keeshan as Aesop. (Talk about bringing things full circle with that last one!)
And that's just a partial list.