I've been considering the Slashdot moderation system, and what's wrong with it.
The main problem, I believe, is that it lets people choose which posts to moderate. This is practically a recipe for assholedom.
Here is how a forum moderation system ought to work.

1. A pool of moderators is chosen in much the same way as now. The most recent userids, people who stay on continuously and those who have recently moderated are excluded. From the remainder a random set is chosen, and those in that set who are currently logged on are used as moderators for the following steps.
2. Each new post is vetted by a small number of moderators before appearing. The moderators are only asked whether the post is an attempt to contribute or not. Reasons should be given, for use in metamoderation. If a majority say it is, in it goes.
3. The post is given a boost in its score while unmoderated. This ensures that people will see it and post comments correcting it or arguing with it if wrong. After a certain number of people have viewed the post, the score boost is removed and final moderation begins.
4. The entire thread containing the post is offered to a small number of further moderators. They are allowed to moderate the post up or down (probably by less than a whole point) (with the score after previous moderations being shown).
5. The end.