I like to take a long phrase (usually some lyrics from a song) and convert it in to a mnemonic. By combining the first letter of each word in the phrase, and converting some of them in to numbers or symbols, I am left with a relatively secure password that it easy to remember.

For instance...

"Cause I know that time has numbered my days And I'll go along with everything you say"

Becomes...

ciktthnmdaigaweys

Becomes...

c1k77hnmd41g4w3y5

I use this system for all of my passwords. I try to use a different password as often as possible and never have to write them down. Frequently used passwords have gotten to the point where inputing them is an exercise in muscle memory.