Celerity - A Ruby wrapper around HtmlUnit.
doh.robot - doh.robot, dojo.robot, and dijit.robot (might be the same as DOH)
FireUnit - A plug-in for FireFox.
JSNUnit - JsUnit on .Net
JsTestDriver - A framework developed by Google
QUnit - Browser based unit testing framework from the makers of jQuery.
RhinoUnit - Ant based.
Schnell - A Ruby wrapper around HtmlUnit.
script.aculo.us unit testing -
SimpleTest from MochiKit -
Testrunner - Don't have much information about this one.
TestSwarm - A framework being developed for jQuery for cross browser support.
WatiN - Appears to be an attempt to bring Watir to .Net
YUI Test - A testing framework from Yahoo!.
Some Useful Links:
Other unit test list
Test Driven AJAX