Short, low security (simple passwords, e.g. a mashup of 2 words or an uncommon word with a typo/1337 edit): Memory
Very very long, or very very infrequently used: Paper slips. Stored somewhere less obvious than a wallet.
Lastly, my favorite:
Long/High security: My hands. No joke. The muscle memory in my hands currently knows about 5 complex passwords that my brain has partially forgotten. The only way I can give someone the password is to pretend I'm typing on a keyboard and tell him what I'm typing.
I lost one of my best passphrases, to Bank of America, because after eight years of having it in muscle memory I became unable to recall it. Two days after getting it reset (to something far less secure, of course) I was typing it accurately again...
Short, low security (simple passwords, e.g. a mashup of 2 words or an uncommon word with a typo/1337 edit): Memory
Very very long, or very very infrequently used: Paper slips. Stored somewhere less obvious than a wallet.
Lastly, my favorite: Long/High security: My hands. No joke. The muscle memory in my hands currently knows about 5 complex passwords that my brain has partially forgotten. The only way I can give someone the password is to pretend I'm typing on a keyboard and tell him what I'm typing.