I use Eclipse 3.4.2 in combination with Flex Builder 3.0. An important feature that is missing in FB3 is a formatter. I’m very glad I found this project on SourceForge by Ernest Pasour: Flex Formatter.
Installing it is easy. Download it, unzip it, move the files to the plugins folder of Eclipse and restart Eclipse. You now see a couple of new icons in your Flex perspective, with the most important being the “Format Flex code” icon. The plugin has a huge number of settings which can be adjusted in the general Properties menu of Eclipse by selecting Flex Formatter.
No more excuses for messy Flex / AS3 code!