Here is a link to the Math Mojo Newsletter that i subscribe to:
There is a really long explanation for why division of fractions works when you multiply the reciprocal. Good to have on hand when you get one of those students (or parents) that want to understand why it works, not just how to do it.
There are also links to other resources. i can't say it is the most informative and detailed newsletter, but i like how he writes and some of the principles he believes in.
Check it out for yourself!