Another man dies today after getting tased: How many dead people does it take before Tasers are recognized as cruel and unsual punishment? Amnesty International reports there have been 150 deaths since 2001 in the United States due to the use of police stun guns.
Amnesty International submitted this October report to the U.S. Justice Department, which actually says over 290 people have died via Tasers since 2001. I'm not sure why there's a discrepancy, though it does include 15 deaths in Canada as well.
In the report, AI also says that of all the deaths, insofar as they could determine, only 25 of the individuals tased were bearing any sort of weapon.