I use Mozilla as my main browser and it has built in pop-up blocking. You can also block all images from a server (to get rid of many banner adds) just by right clicking on an image and telling it never to load any more images from that server. In addition, I turn off some other javascript stuff and set it to only play animated GIF images once. Finally, I don't install Flash for Mozilla.
The result is that my normal browsing experience is quite pleasant. Very few adds, no popups, no flashing crap all over the screen all the time. The tabbed browsing is excellent and it has many other advantages over IE.
Sometimes, I actually *want* to see a Flash animation or something like that (though far less often than I would have guessed) so I keep IE around with all that crap installed and turned on. About once a week or so I have to fire it up to look at a specific page, but the vast majority of the time I use Mozilla and don't have to deal with all the crap.
I'd *highly* recommend this setup to anyone who is sick of the garish nightmare that the web has become.
- Russ