Technical Documentation - Formats, Resources, Standards

We are trying to write technical documentation without re-inventing this wheel. We're sure there are formats, standards, resources out there that others are using, that we could start with.
But it's nigh onto impossible to find any information about it. Seems like the days of the Venn Diagram & Data Flow templates (to quote a few old models) are over. Even Visio skimps on teaching the "How" of doc, focussing instead of how to connect boxes, etc.
We're sure that other companies are generating SOME kind of doc - we want to hear about yours!

Please contact me if you have any ideas for us in this area. We are NOT talking about User Manuals, only about the technical stuff behind the curtain.

Thanks & keep in touch. Annie