Originally Posted by torgone

For future reference:
A 2-liter soda bottle does the trick every time. Fill it completely with water; Holding your thumb over the top(so no water escapes until you get it under water), invert the bottle and submerge it directly down into the toilet as far as possible; Mash down on the end as hard and as fast as you can, collapsing the bottle. The hydraulic force will move whatever is stuck. Your hands will get icky, but you will be clog-free.