A WebmasterWorld thread has discussion on what type of advertiser would you automatically add to your AdSense competitive filter list. I.e. which type ads do you not want showing up on your site?

Here are some of the responses:
Adult Related SitesRingtone SitesWin Free Stuff SitesIrrelevant SitesMFAsDeceptive SitesParked DomainsWork From HomeEtc.

I would create a poll here, but the answers can be so open ended. Which type of ads would you block immediately?

Forum discussion at WebmasterWorld.