Ken Kahn's ToonTalk, a cartoon language with hard-core theoretic underpinnings:
http://www.toontalk.com/
Prograph: http://en.wikipedia.org/wiki/Prograph ... seems Prograph lives on as Marten:
http://andescotia.com/products/marten/
Self's IDE was/is a thing of beauty, talk about Flow (in the Csíkszentmihályi sense)...
Overall, though, I'd have to say Haskell is the most interesting, for the potential adavances in computing that it represents.
