Mike Walker discusses in a recent issue of the Microsoft Architecture Journal a set of tools that can be used to document solution architectures - based, not surprisingly, on Microsoft tools. Together, these make up the Enterprise Architecture Toolkit.
Since I don't have a Windows Server to run Sharepoint (I could, presumably, use Azure), I came up with a similar application setup using open source or cloud-based tools:
The only thing that needs to be built is the manager ("gateway", in the chart above) which can be a RIA application whose role is to tie everything together. Sounds simple enough?