Hahahaha, there's a lengthy discussion on this messageboard;
www.imdb.com/title/tt0418819/board/nest/21022688
about the best way to see of a zombies/some zombies/millions of zombies.
I agree with you, Andy, that a chainsaw to the head is pretty good against a zombie. A shotgun is also a classic anti-zombie weapon (sawn-off of course). Personally, if I managed to divert on or two of them away from the main horde (is horde the name for a group of zombies?), which zombies are 99% of the time found in (they are the quintessentail pack animal) I would fly kick their heads off. This would never work if there were thousands of them though.
Are zombies scared of fire? I forget if they are or not.