This might not be appropriate for this forum but nevertheless.
Ever wanted to use a fisheye lens but been put off by the cost of buying one?
http://www.photo.net/canon/15-fisheye
Well here is a cheap alternative.
1) Buy a door security spy glass.
2) Drill hole diameter of spy glass in middle of lens cap (metal lens cap is best for this).
3) Glue spy glass in place.
4) attach lens cap to normal 50mm lens.
You won't get the sharpest of photos and vignetting is a problem but for around £10 its a winner.