To make sure that the pass phrase chosen is strong enough and offers sufficient bits of entropy it is very important that the words are chosen in really random fashion. This is where Diceware comes into the picture.
Diceware™ is a method for picking passphrases that uses dice to select words at random from a special list called the Diceware Word List. Each word in the list is preceded by a five digit number. All the digits are between one and six, allowing you to use the outcomes of five dice rolls to select one unique word from the list.Arnold Reinhold, http://world.std.com/~reinhold/
As mentioned above, since humans are more likely not to pick up really random words, Diceware is the ultimate solution to solve this problem. Diceware proposes a list of 7776 short words, abbreviations and easy to remember short strings. The words are between 4 to 6 characters which makes those easy to remember. A word can be selected from the list by rolling five dice or rolling one die 5 times. You can get detailed information about how to use Diceware here. The Diceware technique is also endorsed by the creators of 1Password.
The Password Haystacks concepts suggest another way of creating a memorable password. It is based on the idea that length is the most important factor once exhaustive search (Brute-force attack) begins. It suggests that even an easily breakable password like “Password”, once padded with characters of any sorts say “$$$…Password…$$$” can become extremely strong. You can define your own padding scheme which will add sufficient length around simple word you can remember.
Finally, I will leave you to check out this password generator inspired by xkcd comic strip and Password Haystacks concept.