Use a password form. Have a set part, and a variable part. An example (this password form is made up and is not mine)
My first cousin is named Hal. I start all passwords with "H@l". (note that I changed the "a" to the "@" sign).
I then use the first 3 letters of the website. RV.NET would therefore get "rvn".
I then use a number, like the first 4 numbers of my parents' phone number growing up, "3652".
Therefore, my RV.NET password would be H@lrvn3652. Every website would have a different password since letters 4, 5 and 6 would change with every website, but I would only have 3 different letters to remember, and the website name gives me those.