Research
Keep in mind most of the servers I use already have this as a console feature.
http://anyterm.org/demos.html - has demos of the various solutions.
AjaxTerm - python based, claims to be easy to install. Looks very similar to products I have seen used by hosting providers. Has flasshing network indicator.
AnyTerm - Looks comprehensive and has a drop down. Also provided as a service so you don't have to install their software.
Shell in a Box - ".. exports arbitrary command line tools to a web based terminal emulator". (I believe this mean it is all executed on the client).
More comparisons - http://anyterm.org/compared.html#secid2250882