I had a chargen session last night with two players, one of whom has never played an RPG before. (Though he has played computer RPGs, which I found to be of great help, as he was already familiar with concepts such as class, level, hit points, and so on -- not something I'd ever considered before!)
I explained to the new player which game we're playing (Labyrinth Lord), and why it's a clone of another, older game. The conversation developed into a mini history of D&D and its various versions.
Afterwards I had the urge to make a diagram to show the game's history in a nicely understandable visual form. Here's what I came up with.
It's not completely comprehensive, no doubt lacking quite a few clones and sub-versions. Basically I just included stuff I know of. I think it's a fun diagram though :)