Try playing your guitar like a bass. While doing hammers and pulls on the lower strings, slap the strings with your middle finger or thumb. If you have an acoustic, you can also slap up on the frets to get multiple harmonics. It'll sound really celtic and folksy.

If you have a volume pedal and a delay processor, you can try the Satch thing where he makes his guitar sound like a flute . . . like at the end of the 3rd song on the Extremist. With the volume pedal all the way off, reverse your whammy bar so it's back over the body of the guitar parallel to the neck. Pick a note, push your pedal forward, and lightly give it some whammy. You can slide around to different notes while you have the pedal forward too.