Adblock+ does a good job of keeping ads away from my browsing experience. Sometimes you have to dig in a little deeper to find the pattern for ads embedded in movie clips, but so far I've been able to block everything that's annoying. The non-obtrusive ads that remain, I just block mentally.

I use a hosts file for advert blocking, which also stops (some) advertiser tracking - adblock doesn't because it only blocks the display, not the fetch.
Making all plugins click-to-play is good security anyway.
Ed

Privoxy stops the fetch and is quite intelligent.

-Tor