I have seen too many times a system being compromised because of weak passwords.  Here is a list of the top 250 hacked passwords.  If you use anything close to one of these I urge you to change it asap.

http://www.duosecurity.com/docs/top250gawker.txt

About.com has a nice short article about how to create a secure password.

http://netsecurity.about.com/cs/generalsecurity/a/aa112103b.htm