Aptana is a cool, open source Eclipse plugin that a co-worker pointed me to.  It’s a HTML/JSP editor with lots of JavaScript capabilities.  The syntax coloring is good and it lets you know if you have invalid HTML.  Autocompletion works with both HTML and JavaScript.  Adding Aptana with the Eclipse Webtools Project make a very good combination — you get the syntax coloring for JSP’s that WST lacks and WST can tell you what JSP errors you have in your page.

Aptana seems to have lots of cool AJAX abilities but I haven’t messed with that.  I just use it to hack at JSP and JavaScript.  It would be neat to start a AJAX project with Aptana from scratch and see how it works.