I've always been a fan of adding chromatic notes between the strong notes of the pentatonic. It works great for shredding palm muted heavy distortion, as well as adding a Jazzy feel to your improvisation.

The principle is to add the "extra" notes in between the major second intervals of the scale and leave the minor third intervals as is. For example, on a A minor pentatonic (A,C,D,E,G) to add the passing tones C#, D# and G# so you'll get a scale (not really a scale but a group of notes) that goes like this: A, C, C#, D, D#, E, G, G#

Try to mess with it - it's really cool!

Here's a few exercises I wrote to illustrate - using a descending motion of all the pentatonic positions with the passing tones.