I’ve been looking for a way to get feeds from all tags, automatically generated. At first I thought that I had to write a own piece of code or use an already written extension. But after searching for a while I fortunately discovered that the function already exists.
If you want to get the feed of e.g. posts with the tag english you go to http://www.qense.nl/tags/english/feeds. This trick can also be used for categories.
You never stop learning. 😉
EDIT: I just discovered that it works for all things. If you just add /feed/ to a WordPress url you’ll get the feet for the posts displayed at that page. That means you can also get feeds from an archive.