StumbleUpon lets users rate sites with a thumbs up or down as they browse around the web, forming a massive database of recommended sites, and clicking "Stumble" on the site's plugin bar takes you to a random one of these sites.
2. Type related:url into Google
Google may not yet be sentient but it certainly has a handle on peoples' search behaviors. Just type related:theurlofyourfavoritesite to see what other people are looking at.
3. Test out your Hunch
Hunch is a user-powered recommendation engine. Users rank stuff they like, Hunch spits out results based on collective user knowledge. Lots of community action and listmaking here, if that's your kind of thing.
4. Play around with SimilarSites
SimilarSites bills itself as an alternative to fruitless Googling. Users start with the familiar and refine their results as they learn more about what they like. Sites are categorized and rank, making it easier to explore with just a few clicks.
5. Install a plugin
SimilarWeb is the plugin version of SimilarSites, with the added benefit of working automatically as you browse around the web.
Grab the plugin for Firefox, Chrome and Internet Explorer here.
How do you find new, cool and interesting sites? Share your tips and tricks with us in the comments.