Well over a year ago there was a major security breach at a site called RockYou.com. One of the interesting outcomes is that the breach offered the opportunity to analyze password behaviors since over 32 million passwords were revealed.
Here is the top 20 list and if you see any of your passwords on this list, its a good time to think about using stronger passwords!
Strong passwords should include uppercase and lowercase letters, numbers, and symbols. Your computer security starts with the strength of your passwords, so don't use something that's easy to guess or easy to automatically generate (like a keyboard string or word in the dictionary).