% ps aux| grep Finder.appGet the process ID (the first set of numbers in the output) and then type:
% kill -HUP 1234Replace 1234 with the actual process ID of the Finder from the first command. This will re-initialise Finder and gets rid of the beach-ball. BTW, this was on 10.2.4, so some of these Finder bugs are probably fixed, buts it's a tip worth knowing.
[robg adds: When the Finder locks up on me (hasn't happened yet in 10.3), I just use Command-Option-Escape to force it to re-launch; this works without requiring a trip to the Terminal. You may, however, have to switch from the Finder to another app before the Command-Option-Escape key sequence will be recgonized.]

