Something like IEEE 1471-2000:
http://standards.ieee.org/reading/ieee/std_public/description/se/1471-2000_desc.html
or an EA framework like TOGAF:
http://en.wikipedia.org/wiki/TOGAF
would be tough slogging.
I'm interested in hearing from others what they use. Sharing of templates even better!
My views on documentation are in close alignment to this post:
http://traceinthesand.com/blog/2006/08/25/architecture-documentation-courage-to-fly-in-the-face-of-convention/
Cheers