"Thank You"

[hockeyophile.livejournal.com]

Does anyone know the origin of the Russian word "spasibo" (sorry, my computer is crazy and I just can't install Cyrillic onto the system), meaning "thank you"? I'm familiar with most of other Slavic languages enough to notice that they use a form from their word meaning "to thank" (Czech 'dekuju' and Bulgarian 'blagodarya', as just two examples), however, "spasibo" looks nothing like the Russian verb for "to thank" (which is similar to the Bulgarian word). Can anyone tell me the origin of "spasibo"? Thanks!