I've just pushed a very nice patch from Chin Fang that allows host ranges in the inventory file.
It looks like this:
[webservers]
foo.example.com
www[001:050].example.com
If you put leading zeros in there, it will keep the leading zeros, if you don't want them, don't include any leading zeros. I modified the patch slightly so the range is inclusive, not exclusive. (www050.example.com will be in the list in the above example)
I'll include this in the docs once 0.6 releases.
--Michael