One of the most interesting browser add-ons I have encountered so far is www.stumbleupon.com
The short description taken from their website says
StumbleUpon discovers web sites based on your interests.
What I found especially compelling to me as a software developer is the ability to find web pages based on my interests. For example I can go from one computer related page to another, the nuance is in that somebody has recommended the page! This means the site is worthy to take a look at. In case I do not like the content or do not find it accurate I simply vote it as not recommended. After using this service for about a year I have built en enormous amount of links in my customized by topic Bookmarks menu.
Go ahead, check StumbleUpon out today!
Happy stumbling!