Personally I was reading the pi-calculus book just last fall, and found jocaml to be very interesting, since it implements a variant of the pi-calculus (called the join calculus). Concurrency constructs embedded as operational semantics in the language definition of the lambda calculus is really brilliant, the implications are rather difficult to reason about however (which is truthfully beyond me at this point, but I'm getting there :)). Did you ever read anything like that?