Scanline Counting Method
axd: I'd like to mention a method I use when manually estimating the score; it is not "combat-proven" yet, so I prefer to mention it here rather than on the main page, so it can accumulate some reactions before considering promotion for the "grand public".
The "scanline" method is derived from the way electron rays scan a TV tube.
The idea is to make one pass for each player: systematically count from left to right, starting from the bottom left corner, work up in each column in turn (or any other preferred origin/direction) and count only in that player's territory (2 points for dead stones); end with captured stones and komi if that player has komi. I use this together with Steve Fawthrop's memorization trick.