Adblock Plus is one of the most popular and well-made ad-blocking extensions.
The extension removes annoying things like banner ads and pop-ups from your web experience. That may seem like a slight difference, but visiting some sites that tend to be bogged down, especially with pop-ups, can be liberating. But if you do choose to use it, make sure to "white list" sites you feel don't have an intrusive ad experience — especially those who make their money on advertising revenue.
AdBlock Plus also works with Safari, Opera, and Firefox if you don't have Chrome.
Download Adblock Plus here.