I get bored sometimes and start drawing up a Harry Potter family tree. It's insane how many connections there are, how many familiar names you can happen upon. Check it out (and click to view large, please!):
A couple of notes I found on past editions I've done:
*Dorea and Charlus were probably not James' parents but rather his grandparents - this makes the dates fit better.
*Also, Lucretia and Ignatius were probably Molly's grandparents - the generation missing from this particular map may include the famous Auntie Muriel.