http://feedvalidator.org/

This is a free RSS feed validator. Make sure and run the feeds you intend to use in your app through this before you hit "publish." It is a great way to make sure you don't have some "oopses" (that's a technical term) in your feed. Remember, the simulator is *not* a perfect representation of what your final app will be. This Validator will make sure you don't have any data source surprises.

Cheers...