I implemented opt-in "rich content" Clojure REPL interactions in nREPL (a tool-agnostic network Clojure REPL server & client implementation), with a first spike of client support for such "rich content" in Counterclockwise (the Eclipse Clojure plugin). The result is something that I think can be the basis for breaking a lot of new ground in how we use the [Clojure] REPL. This is a video demo, with some discussion of the implementation and ways clients can add their own response types and such dynamically.

For more, go to cemerick.com/2011/10/26/enabling-richer-interactions-in-the-clojure-repl/