Aptana the new Javascript and CSS IDE
Writing Javascript code is tedious with Visual Studio. no Intellisense or really little, and when you mispell any method plus all the case sensitivity issues, you are wasting a lot of time there.
I just discovered a new kid in town called Aptana (Beta version at the moment) which is a very promising IDE for typing Javascript and CSS.
Aptana has some cool features like auto completion with a full glossary of DOM methods and properties but it also can understand libraries like Mochikit, Prototype, Dojo and more.
Download here