Recommend a free ad blocker?

Hi guys,

I've had the K9 software for a while now and find it great. However I'm still getting occasional tempting ads on websites. Ads like posters in real life are fine, but being on a web page is too close to the 'danger zone' for me atm.

Being a bit of a tech noob... Can anyone recommend me a good software that will block all ads (or most of the ads) for free? Thanks