There is a cool MXML and Flex AS3 automatic code formatter that some cool guys published on SourceForge.
I was having a hard time getting it installed the manual way, so here is the easy way:
1) In Flex Builder (standalone or Eclipse), go to Help->Software Updates->Find and Install
2) Choose “Search for new features to install”
3) New Remote Site
4) Name it whatever you want and use this as the URL:
Now hit next a couple of times and you should see it downloading and installing. It will recommend that you restart (good advice), and then you’ll know if it installed because a) you’ll have some new toolbar buttons, and b) you’ll have a new “Flex Formatting” option in “Flex Builder->Preferences”