E Power Chord = E5 = E and B
To solo over an E5 vamp, you can use any scale or mode that contains both E and B. It's that simple!
You can use
E Lydian - E, F#, G#, A#, B, C#, D#
E Ionian (major) - E, F#, G#, A, B, C#, D#
E Mixolydian - E, F#, G#, A, B, C#, D
E Dorian - E, F#, G, A, B, C#, D
E Aeolian - E, F#, G, A, B, C, D
E Phyrgian - E, F, G, A, B, C, D
These are the E Modes that have a natural 5th (B). Notice that they are similar, but they all give different results.
E Harmonic Minor - E, F#, G, A, B, C, D#
E Melodic Minor - E, F#, G, A, B, C#, D#
E Phyrgian #3 - E, F, G#, A, B, C, D
These are three other scale choices. There are MANY others. Just use anything with both an E and a B.
Have fun trying these out.
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster