This is a list of sites you can use to interactively try out programming languages online. Read more about REPLs at Wikipedia.
Some of these sites aren't strictly REPLs since they don't maintain state, those sites are probably more accurately described as "REPs"?
Am I missing something? Let me know.
http://dabuttonfactory.com:8080/
http://jonathan.tang.name/files/arclite/
http://colabv6.dan.co.jp/lleval.html
http://tryclj.licenser.net/ - http://www.try-clojure.org/
http://jashkenas.github.com/coffee-script/ (Click "TRY COFFEESCRIPT")
http://colabv6.dan.co.jp/lleval.html
http://www.solve-et-coagula.com/As3Lisp.html (subset)
http://colabv6.dan.co.jp/lleval.html
http://trygroovy.appspot.com/tutorial
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
http://www.squarefree.com/shell/shell.html
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
http://cappuccino.org/learn/console/
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
http://www.datamech.com/devan/trypython/trypython.py
http://colabv6.dan.co.jp/lleval.html
http://doc.pyschools.com/console
http://pythonwebconsole.thomnichols.org/
http://sisc-scheme.org/sisc-online.php
http://colabv6.dan.co.jp/lleval.html
http://colabv6.dan.co.jp/lleval.html
See also:
http://stackoverflow.com/questions/49092/online-interactive-consoles