On the Smashing Magazine site there's a post some of Paul Tero's favorite programming mistakes he's come across and heard of in his time programming.

I like to classify these mistakes into three broad groups: cock-ups (or screw-ups in American English), errors and oversights. A cock-up is when you stare blankly at the screen and whisper "Oops": things like deleting a database or website, or overwriting three-days worth of work, or accidentally emailing 20,000 people. Errors cover everything, from simple syntax errors like forgetting a } to fatal errors and computational errors.

Included in his list are things like:

• Leaving Debug Mode On
• Turning Debug Mode Off
• Wrong Variable Type
• 1p Errors

Examples of each are included with both code and descriptions as well as "lessons learned" to help you not make the same mistakes in your applications.