Scriptblock + flashblock on Firefox. I still see Google adwords which aren't so bad (they don't take up download time) but I skip all the other annoying shit. I hardly see any ads with this setup even though it's not specifically blocking ads, most of them happen to load with some javascript or flash. I can selectively enable specific scripts or flash content by just clicking on them, so I miss all the annoying popups and prevent pages from trying to grab control away from the browser.