Unbiasing of sequences

There is the well-known method of unbiasing of bit sequences due to von Neumann. Are there similar schemes applicable to other sequences, e.g. the result of throwing a normal die?

The following simpler adaptation of von Neumann's trick is more efficient than the one described in HdM's answer. Throw your die twice. If the two answers $x,y$ are different, write $0$ if $xy$. This way, you get an unbiased bit source. If you are so inclined, you can use this bit source to simulate fair die throws.

StackExchange Computer Science Q#9469, answer score: 4