REcently had to change a password, which reminded me of my constant amazement that more people don't use acronyms to form personally memorable, but not obvious passwords, which can be extremely resilient in length.
Letter component:
Personality: I love bacon more than anything else in the world, except beer: ilbmtaeitweb
All girls are lying scum who take you for everything they can get then boff your best friend: agalswtyfetcgtbybf
Hang gliding is the purest bliss in the world: hgitpbitw
I love my partner with everything I am, and I would die for my kids: ilmpweiaaiwdfmk
Potitics: Free handouts are killing our country, killing job creation, killing personal motivation, ambition, and success: fhakockjckpmaas
Gays are human, sexual, loving, family, marriage is their right: gahslfmitr
Bush took us down the sink and Obama isn't helping: btudtsaoih
Religion: The Lord is my shepard I shall not want: tlimsisnw
there is no god but Allah and Mohammed is his Prophet: tingbaamihp
in the beginning was the big bang, biochemical evolution arose from physics, and now the universe sees itself: itbwtbbbeafpantusi
Pop culture: A Song Of Ice And Fire, A Game of Thrones: asoiafagot
The Empire Strikes Back, Bladerunner, Alien, The Matrix, Avatar: tesbbatma
Mad Men, Dexter, The Big Bang Theory, Modern Family, Generation Kill: mmdtbbtmfgk
Number/Symmbol component:
symbols can be constricted, but if you have free reign, you can do emoticons and ascii art: =p :x =) =^-^= (#_0) (o(O_O) >_<
As for numbers, birth dates are obviously right out. If you are into number symbolism, then you could go with things like 0 for everything, 123 for the Holy Trinity, 4 for the number of the physical world, 6, 8 and 9 if you are into Chinese numerology, 7 if you are into western mythology concepts of the divine and moving between worlds.
Or you could go for memorable dates or years that are more personally known. The date, or the age you were when you lost your virginity. Or went through some other life altering event. The number of trees in your yard: 4, and the number of stories on your house: 2, the number of rooms in your house: 6, the number of cars your family owns: 2. Numbers that mean something to you, relate to each other, tell a hidden story about yourself.
Anyway when I can guess my Dad's password immediately and first try, when asked by an official... people just aren't thinking things through enough.