Take off enough cassettes and you learn the value of a quality chain whip.

The Park Tool SR-2 Chain whip is the best chain whip on the market. Built from tool grade steel with an extra long handle and high quality chain it will loosen the most suborn of cassettes. While cheaper tools are available you cannot put a price on a chain whip that holds together after years of use. 

15inches long and works on cassettes 7, 8, 9, 10, and 11 cog systems.