You can also recommend sites you visit to others, connect with those who have similar interests to you and visit Web sites others have recommended. All in all, this is one of those add-ins that you'll either hate or love. If you like social networking sites and discovering new sites in a leisurely fashion, you'll enjoy it. If not, you won't see its point.

del.icio.us

You've probably heard of the del.icio.us site—though you may not have a clue what it's about. Like StumbleUpon, it's a hybrid that combines Web surfing with social networking. At its most basic level, it lets you bookmark sites and apply tags to them, so that they're later easier to find by searching or browsing through keywords. The bookmarks and keywords are stored online, rather than in Internet Explorer, so you can access them from any computer.

You can also share bookmarks with friends, family and co-workers and see bookmarks they share as well. And you can also see what sites have been bookmarked most frequently by other visitors to the site, as a way to find new and interesting sites. In addition, you can browse through sites that have been bookmarked based on tags—for example, see the most popular sites tagged with the words Internet, Java or politics.

McAfee SiteAdvisor

If you're looking for an all-in-one security add-in for Internet Explorer, this is the one to get. It's particularly useful if you want to make sure you don't visit potentially dangerous Web sites or sites that may host spyware.

Whenever you visit a site, the SiteAdvisor button turns green (for safe), red (for dangerous) or yellow (possibly dangerous). Click the button for details about the site's rating. In addition, when you do a search on a site such as Google, a red, green or yellow button appears next to each individual result. The add-in does more as well, including a warning about potential phishing sites.

Preston Gralla is a contributing editor at Computerworld.com, and the author of more than 35 books, including How the Internet Works.