Chrome: Adblock Plus is a popular extension, but it's memory hungry, and it can slow your system down. If you want to try out a leaner alternative, check out uBlock.
uBlock works on any Chromium-based browser. Once installed, the app works very similarly to Adblock Plus; it will block ads for you, uses the same source lists, and keeps your browsing experience clean. As with any extension of its type, the add-on requires heavy permissions to work. The developer explains those permissions in detail here, and answers questions about the tool and its features here (including comparing it to ABP). If you're curious how much memory you're actually going to get back his efficiency comparison is a good read too.
Also, we've said it many times before, but it's worth remembering -- without advertising, most online publications wouldn't survive, so you should be selective in how you use them.