Careful with the Google toolbar...apparently it installs a particularly nasty bit of spyware. There was a thread about this a few months ago but I wasn't able to find it by searching on "google" or "toolbar".

I use WebWasher. It's free, and it stops popups cold. Much better than PopUpKiller, which made annoying noises and didn't work very well. AdAware is also very good, but it's best at cleaning out unpleasant spyware and data miner programs that have insinuated themselved into your computer, not at blocking popups.

Happy surfing!

Aloha,
Mark