E Myxolidian Backing-Track.

There are some recognizable and easily found songs here: http://en.wikipedia.org/wiki/Mixolydian_mode#Notable_songs_in_Mixolydian_mode

You may already understand that the Mixolydian mode is simply the scale based on the 5th note or V ("five"), also called the dominant, of a given major scale. For example, if you know how to play a given major scale, say C major, you already knkow how to play a G Mixolydian scale! Just play the C major scale, but from G to G. Easy.

You may find this helpful: http://en.wikipedia.org/wiki/Tonic_%28music%29

A quick little search helped me realize you can and should play riffs in this scale over a dominant seventh or V7 chord ("five-seven").

The first place that came to mind is the beginning of a chorus (or lead-in to the verse) that uses the V7 (or its close relative the ninth chord, more common in jazz).

There is a thread worth checking out here: http://www.ultimate-guitar.com/forum/archive/index.php/t-750701.html (Click on the link by "Full Version" if you would rather see the blue and gray UG site.)

In that thread, user "Archeo Avis" has solid input and seems to have a deep background. User yMSamurai's advice is a little inaccurate, so beware.