Note: The new recommended way of having a Django Templates Editor is by using LiClipse: http://brainwy.github.io/liclipse/ (which is a commercial counterpart made to keep PyDev supported, as such it has PyDev standalone and a bunch of other goodies builtin).
Aptana Studio 3 still has PyDev and its own Django Templates Editor, but the bundled PyDev version is not kept up to date.
Below are more details on the integration on Aptana Studio 3 (using the Aptana Themes)
The highlighted tokens are the ones defined in the templates in the "Django tags" context (so, tags to be highlighted can be added or removed).
Also, there's code completion based on templates for the django-templates related stuff and pretty nice html completions inherited from the Aptana html editor.
The image below shows the html completions, a django-templates template completion and its result and a django-templates template completion for the filters.
That's it for now. Please grab it and let me know if it's working or if there's a bug lying around there so that it can be fixed before the official release :)