This is a very interesting article from Lifehacker about how to crack people's passwords, including a top 10 list of the basis for your current password. There are a bunch of tips on how to secure your password and a nice diagram that shows based on password length the amount of processing time to generate every possible combination of passwords for only lowercase letters versus all characters. You can see the dramatic increase in time that it would take a hacker to crack your password combination when you use all or a combination of characters including upper case letters, numbers and special characters.
Here's the article.
If you want to check how strong your current password is, go here to Microsoft's Online Safety Password Checker to find out.