The other 'prepared' format that's loads of fun is 'record pizza'.
Try cutting up some LPs, etc in thirds [or quarters etc] and glue them
back together with aroldite/super glue or something similar, weight
the stylus down with some coins and you get some great loops of the
roughest kind...try and use records of similar thickness so as not to
totally destroy your stylus.
Ian Andrews [sydney] also did some great off-centre hole drilling on
some LPs which gives a nice warping sound effect, kind of like being
sea sick...
t