Watch the Learn To Mix in those Tasty Mixolydian Licks online guitar lesson by Jeff Scheetz from Blues Jam Survival Guide
For a different sound over Dominant chords try the Mixolydian scale. You can really stretch out and get out of the "pentatonic box" and into modeville. The Mixolydian is just the Major scale with a flat 7, which is why it works so well over Dominant chords is because they too have that flatted 7th note. Of course knowing all of your modal scales helps with the fingering on this, but even if you are strictly a Pent player you can incorporate this.