The Android Market has a bunch of mini development environments. On my Galaxy S, I have a Clojure REPL and two little apps for Ruby and Lua "development." Of course, you wouldn't want to do anything serious directly on the phone, but it's nice for trying out little things when you have an idea while you're out.
Yep. Clojure, Lua & Retro. The last is crap and I can't wait to get a real useful FORTH on my Android.