[Bloody Sam Roberts]

Actually, Spybot Search & Destroy might be a better choice for the more aggressive types of adware. Plus it is currently being updated and will catch the new stuff, where AdAware is not and won't. I've made the switch and am much happier with SPybot S&D. It gets the stuff out that AdAware missed.

[tomkat]

actually, AdAware 6 has been out for about a month now.
nicer UI, more control of options, and still free.
paid version does auto-updates and runs AdWatch as a realtime monitor.

AdAware 6

[martin_fierro]

DItto #5.

Spybot S&D works really well.

[jgrubbs]

I agree, I used AdAware untill I recently found SpyBot Search & Destroy. SpyBot removed things that AdAware didn't, and it has a great Immunize feature to protect the sytem from getting more Spyware.