Very often you need to find more similar sites to the one you already have: either for backlink pitch or to compile a link baiting list or just for your niche research. So today I am sharing a few short tips on how to find more related sites (apart from searching Google for relevant terms):
Find related sites linked from similar sources

[related:] advanced search operator looks for “co-citation”, i.e. pages that have similar backlink sources with the one submitted.

This search turns particularly useful for newly launched viral projects because it allows you to find sites with similar concept.
Find related sites tagged by same terms

Similicio.us shows which domains your site can be associated with based on the preferences of those who bookmarked it.

This tool allows you to understand what the site can be associated with based on Delicious users.