While the best improvement is probably not having any, Esther Derby's piece on improving meetings is very constructive and helpful.
Sometimes, stronger measures are called for, though. A favourite from a former workplace was the sound clips that made the rounds to be played on conference calls -- most notably, the one that'd be heard whenever discussion got sidetracked onto stuff that should really be dealt with outside the meeting ("♪♬ Rrrrraat Hoooooole! ♫𝅘𝅥𝅯")
Personally, I'd like to see meetings required to use Parliamentary rules of order and address. It'd reemphasize what a waste of time the meeting is repeatedly throughout its duration; possibly best of all, anyone can move to end the meeting and if a simple majority agrees -- done! Besides, wouldn't your meetings be more tolerable if they were punctuated by bits like "Mme Speaker, I rise on a point of privilege!" and "The Hon. Leader of the Database Team has the floor"? =)