Django templates syntax highlighting in Eclipse
For clarity
Django Templates Editor is only available with Aptana 3.0 and later.  Pydev in eclipse alone does not support it.  Aptana is available as an eclipse plugin or stand alone.
As mentioned by mcoconnor Window -> Preferences -> General -> Editor -> File Associations will give you a list of extensions.  

Choose *.html as the file type
Select HTML.Django Templates Editor (Aptana) from Associated editors
Click Default.
Reload any html files you had open in the editor

This should make Aptana treat the Django specific markup correctly instead of reporting errors and also will offer code completion.
I use Eclipse and pydev for django development. This has worked more or less ok, including debugging. Syntax highlighting doesn't seem to work everywhere though. I couldn't get any highlighting for the templates thought. Is there a way to get the highlighting and code suggestions for the templates?