At $EMPLOYER, I have a script that takes a description of the network topology, converts it to a sequence of Host stanzas and writes them to ~/.ssh/config. The source file is simple enough that the sysad team can keep it up-to-date when they change the network configuration, and most people just have to run the 'update' script occasionally to have Super SSH Powers. It's quite popular.
Unfortunately it's not really self-contained enough to post; the most complicated thing in it is basically a copy/paste of the "Dijkstra's Algorithm" sample-code on Wikipedia, though.
