It's a 3 step process for me. I use a good sharp gasket scraper tool first to get off as much of the big stuff as possible. Then I use a single edge razor blade to get off the next layer. Then I use an abrasive wheel like jeff recommended to finsih it off and get everything shiny.
The only reason I don't go straight to the abrasive wheel is, I have seen times when a chunk of gasket is really stuck on and the abrasive wheel is starting to wear it down but the gasket piece starts to look the same color/texture as the rest of the head and you end up missing it. This inevitably results in a head gasket leak, I also had the same thing happen to me on a differential gasket. Just my .02.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang