http://sourceforge.net/projects/flexformatter/

* System Requirements: Eclipse 3.3+, JDK 1.5+.  The intent is for this software to be used with FlexBuilder 3 or 4, but there are no actual dependencies.
 
* Install (several ways to install)
 
* Add a remote update site through Help->Software Updates:
http://flexformatter.googlecode.com/svn/trunk/FlexFormatter/FlexPrettyPrintCommandUpdateSite.  The
exact instructions differ depending on which version of Eclipse you are using.
You should be able to turn on Eclipse auto updates and
be notified when a new version is published.  You may have to set up proxy
settings in the Eclipse preferences if you are behind a corporate
firewall.  Note: if you are running Eclipse 3.5 and the update site doesn't work
for you, try adding "/site.xml" on the end and see if that helps. 
 
* Download the zip file and extract the 3 plugins jars into the
Eclipse plugins directory (Eclipse 3.3) or the dropins
directory (Eclipse 3.4+) and restart Eclipse (with -clean
if you are using 3.3).  Enough people have had problems with this with Eclipse 3.4+ that I recommend only using the update site.