every Theremin I have ever seen is a sepertae instrument,and not a guitar effect at all...its like an antenna that picks up where your hand is in relation to it, and emits different frequencies accordingly...really cool sounding...the beach Boys used em too...
also, look into so Moog effects...not cheap, but weird
[FONT=Century Gothic]Hope is when we feel the pain that makes us try again[/FONT]