Unless you are running the new experimental search interface on Google, you can make use of a feature called similar pages directly on the search results page. This feature displays a list of related, or similar, websites, directly in the search results. Say you are fed up with Google Search and want alternatives. Instead of search for Google alternatives, you would search for Google and click on the Similar link next to Google’s search result.
The new page that opens suggests among others Yahoo, MSN, Ask and Bing.
While it is fine to search for similar sites directly on Google, it often is not as handy as it could be. Why? Because to use it, you need to use Google Search. It works fine as long as you know the site that you want alternatives for. If you want to find sites like Google you are fine. But what if you do not know the site yet?

You would have to load the site first to see if it offers contents that you are looking for. Afterwards, you need to return to the search results listing to click on the Similar link to find related sites.
Google Similar Pages for Chrome addresses this issue. The Google Chrome extension adds a button to Chrome’s address bar that displays four related results directly on the active page.

Instead of having to go back and forth between sites and search results, you can utilize the similar feature right on the sites.
Sites are displayed with a thumbnail, name and short description. You can click on a result to open the suggested web page in a new tab.
The only downside of the extension that it limits the suggested alternatives to four sites, with no option to display additional suggestions or open Google’s related sites listing.
Still, the top four results are often good enough matches, and you can use the extension again on their pages to find additional related sites.
Chrome users can install Google Similar Pages from the official Google Chrome extensions repository.
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I find SimilarSites to be more feature full.
At least with Firefox (my default) as i can add it to the search box and install the SimilarWeb extension if i want more.
http://www.similarsites.com/
and… results aren’t limited in number.