Aptana is a new IDE (embeded in Eclipse for now). If you already use Eclipse 3.2, you can just install the plugin from the update site: http://update.aptana.com/update/. Lots of good stuff: HTML, CSS, and Javascript code assist, etc. I’ve use it a bit and it seems likely to become a part of my development environment — lots of productivity enhancements. Now I can write twice the number of social bookmarking sites as before. 
The documentation is also very strong. Just check out all of the tutorials for using Aptana with various AJAX client frameworks:
- Creating a new AJAX library project
- Enabling Code Assist to work with AFLAX
- Getting started with Aptana and AFLAX
- Getting started with Aptana and Dojo
- Getting started with Aptana and MochiKit
- Getting started with Aptana and Prototype
- Getting started with Aptana and Rico
- Getting started with Aptana and script.aculo.us
- Getting started with Aptana and Yahoo UI
None too shabby.
