i wouldnt advise you to pay for a program that stops them, as it cannot stop all of them.
But, you can get the GOOGLE TOOLBAR

it simply puts a very small bar at the top of your internet pages and is fantastic at stopping popups. i downloaded it a month ago and it has already blocked 2400 pop ups.
You can also click it so that it doesnt block pop ups from certain trusted sites, which sometimes you need.

It is well worth it for free, and it is not even 1mb so even 33k modems can have no trouble