Free+Podcast

http://www.calculatorsoftware.co.uk/classicmistake/reviews.htm

This is a great math podcast. It explains many classic mistakes our students do in math class. It explains mistakes made in may different topics including the Pythagorean theorem, discriminant, adding, and negative numbers.

I use this in my class room as a warm up. It helps students get hints on common errors made by students in many different types of math problems.