Recently I started working on some ASP.NET UI with moderately complicated javascript, and I thought I'd give Aptana a try. Aptana is a (relatively) new IDE for dynamic javascript-based sites, built on top of Eclipse. To cut right to the chase I think it is a GREAT IDE for javascript development, with pretty much zero learning curve. The intellisense which shows if the method/property you're thinking of calling is supported in various browsers (see screen-shot below) is a compelling feature. The only minor annoyance was that the “completion” key sequence for intellisense was CTRL+ENTER, whereas in VS it is SPACE, and try as I might I couldn't seem to customize that key binding. If you're doing anything with client-side script in your web apps give it a try. I'll have to check out the expression web designer beta next and see what's cooking there.
