Two words...

Password Manager

Personally I use lastpass.com and have used roboform in the past but there are many more out there. You just need to remember one very secure master password then the rest you let the PW Manager handle it for you.

I have no idea what my password is for just-dice, or this forum without looking at my password vault! None are the same, all unique, and all very long with letters, numbers and symbols in them.