That is a result of Google Analytics and Google Adsense. These track which sites you visit, which search terms you enter, and then load advertisements which are relevant to these results. There are many different ways to block those.

--Adblock + now has certain cookies whitelisted. Adblock Edge does away with mandatory whitelists. However, IIRC Adblock Edge has issues with Ghostery.
--NoScript blocks javascript based cookies that Adblock+ does not. It can also be used to disable Javascript entirely, though this often causes problems with loading the site/site functionality.
--Ghostery

--For Safari, there are Incognito and Lil-Snitch (both do basically the same thing, to my understanding)