lots of stuff out there, ad-aware, not my choice for bes, but it works. Or try analogx.com they've got some freeware software to get rid of ads, but you have to do work to get these programs to keep the ads from popping up.
I use Pop Up Stopper, which is free and works well. Or you could just go to cnet and run a search and compare a few programs and see what has the features you want: http://www.download.com
The combination of increasing my windows security settings higher than the default and adaware has cut way back on my popups. While I still get flodded when visiting random generic porn sites my surfing is now 95% popup free.