One vote for Erlang - sending messages between processes on separate machines after only a few hours reading Programming Erlang truly had that magical "whoa" factor I remember from days or yore.
I do love Smalltalk (I'm reading SICP). Can it do graphics/UI stuff? One measure of joy in programming for me is to be able to easily build a simple side-scroller. I'll have to get a Mac to try Cocoa I suppose.
It sounds like you might like Smalltalk or even XCode and Cocoa (Interface Builder, etc.).
Erlang/OTP and Erlang web stacks (Mnesia/CouchDB, Yaws/MochiWeb) are a lot of fun.