Here are some tricks that I use......

Try holding a cell phone or a pager up to the pickups. Different types will produce different strange noises. My pager makes a beeping sound, while my cell phone will produce a very strange noise that sounds like a cross between feedback and harmonics.....I stumbled across this when I had my pager on while I was playing. It took me a while to figure out where the beeping was comeing from. This made me try holding every battery powered think I owned up to the pickups.

Allen wrenches used as a slide makes a weird sound too. Not my trick, Tom Morello of Rage against uses this trick. Tom Morello is the king of guitar tricks.

Use a mic stand as a slide.......

I'll add more tricks later.