Use letter replacement to add in symbols and/or numbers that look similar to a certain letter. For example:
a = @ or 4
s = $ or 5
e = 3
i or l = 1 (one)
t = 7
o = 0
Many instant messaging screen names fit the password requirements. While it's probably not a good idea to just use your screen name verbatim, it may give you an idea of where to start.
Example: my screen name, MispaintedMoose (don't laugh) could become Mispainted47moose
Take a short phrase and replace characters where necessary. For example:
"I like rice" becomes iLikeR1ce
"21 Choices" becomes 21Choices
"Catch 22" becomes catch-22
Take the first letter of each word in a sentence and then do some letter substitution. For example:
"My very big dog smells like dill pickels." becomes Mvbd$ldp
"I am taking an underwater basket weaving class." becomes I@t4ubwc
Other brainstorming examples: (don't actually use these)