Most of these ad and pop-up blockers are freebies or have free trials, so give one a go. If its performance isn't up to your standards, uninstall it and try others until you find one that's a perfect fit with the way you browse.
Browser add-ons and extensions
Take it from Firefox fanatics: if you want to stop ads, use Adblock Plus, one of the most popular Firefox extensions around. Installation is a cinch - just download Adblock Plus, and while you're in Firefox, click Install Now.
Once the free extension is installed, it blocks pesky online ads based on their source URLs, so if you're not interested in fiddling, you can just let Adblock Plus do its thing.
Undoubtedly you'll run into an ad that wasn't blocked (or an image that was but shouldn't have been). Just right-click on the ad, select Adblock Image from the context menu, and blast the ad into the bit bucket. And if you're a tweaker, you can bring up Adblock's Preferences (also from the context menu) and create your own filter rules.
For more on lots of cool Firefox add-ons, check out 15 Mozilla Firefox tips & tricks you don't know.
Download Adblock Plus
Google Toolbar Pop-Up Blocker
You probably know the Google Toolbar as a terrific search tool for Internet Explorer or Firefox. But it also comes with a free pop-up blocker that works as well as some of the pricey ones do; it's amazingly accurate at diagnosing and blocking pop-ups that we don't want to see while letting "good" pop-ups appear.
The toolbar supports web-based bookmarking, and throws in a spelling checker and an automatic form-filling feature.
You say you're using Firefox? No sweat: a version of Google Toolbar is available for you, too.
Download Google Toolbar
Yahoo's free Toolbar fits snugly into your browser, right under the address field, and protects you from pesky pop-ups.
Unfortunately, it doesn't do anything about the other annoyances, namely banner and Flash ads. If you don't find those bothersome, however, Yahoo's customisable Toolbar might be the choice for you.
It's loaded with other features, too, including competent Web searches, the ability to check Yahoo Mail, and free Norton antivirus and antispyware scans. The Yahoo Toolbar also lets you create web-based bookmarks that are separate from your system-based bookmarks, ideal if your other browsers also have the Yahoo Toolbar installed.
Using Firefox? No problem - Yahoo has a Toolbar plug-in for you, too.
Download Yahoo Toolbar
IE AdBlock is a small, unobtrusive, set-and-forget freebie that removes many but not all pop-ups, banner ads, and other annoyances. Unfortunately, the tool doesn't know how to handle Flash ads, and it doesn't give you a way to modify the blocking filters.
Download IE AdBlock
If you want a smart, free add-on for Internet Explorer, download IE7Pro. The free tool has tons of ways to make IE easier to use, and you can access everything via one button in the Status bar.
IE7Pro stomps on banner and Flash ads (it successfully removed most ads of that type from the sites we visited), but it has a tougher time removing pop-up ads; in my tests, most pop-ups passed through like water through a sieve. But IE7Pro isn't just about ad blocking.
The tool provides helpful functions that plain IE doesn't, such as Super Drag Drop, a way to drag a link to any spot on the page to open a new tab, and Mouse Gestures, a cool feature that lets you scroll, open, close, and navigate through open tabs. It also has a built-in spelling checker and a handy recovery feature just in case IE takes a nosedive and crashes.