Like someone else posted upthread, I have a "In case I die" document that has links to all my passwords and account numbers - where assets are, debts, etc. I don't want anyone to have to weed through papers and wanted everything orderly. (Not that I'm planning on dying anytime soon, mind you...)
You might remember, I posted about this a while ago. Another thing that I read that I thought was a good idea was if you have a generic password, one way to change it is to use the first two letters of the site you're on.
So if my password is password1, my Nest password would be password1NE. I thought this was clever.