SimilarSites.com

This site makes it easy for you to find an alternative site to those you like.
The sites are listed in order of significance. So If you typed in facebook then the closest in significance would be twitter with 76% similarity. Even though they're nothing like each other.
It allows sponsored site links to finish at the top of the results so its not perfect.
Overall - A useful tool.

I came across similarsites.com while shopping for a dress online. I went over my usual shopping sites list and I couldn't find anything I liked. So, I hit "similar sites to Zara" on Google and came across SimilarSites website. It worked like magic! I found so many things I liked on sites I didn't know even exist!

I loved the similarsites, a friend had already commented, and soon after I found on the internet through google searches, congratulations on the site and thank you.
Adeus Estrias