You really don't need to protect your passwords from yourself. Really you don't. But apparently most people I know think they do. Because I get calls all the time from friends saying that they can't get onto their home network, or log on to their router, or that old email account they haven't used in a while, because they can't remember what password they used.
So here's a quick tip: keep a log file of your passwords. You don't need to post it for everyone to see. But for god's sake, do put it somewhere where you can find it.
It doesn't need to be a computer file. Frankly, it might be better if it's not, because then if your hard drive dies you'll still have your passwords (because you and I both know you're still not backing up your hard drive). Even a collection of post-it notes in a drawer somewhere is better than nothing.
And about the router password. You password-protect your router to protect yourself from people outside the house, not inside. So do yourself, and your houseguests, a favor and tape the password onto the router. We'll all be glad you did.