I blogged on this topic recently http://onecoolsite.wordpress.com/2009/11/17/link-building-strategy-locating-similar-sites/
Keyword Example "paranormal"
(1) paranormal search engines keyword searches
http://www.paraseek.com/
http://www.ufoseek.com/
http://www.ghostchatter.com/ghsparchives/search.html
(2) similar sites keyword search http://www.similarsites.com/
(3) The 3 big search engines keyword searches : Google blog search for "paranormal"; Yahoo blog search for "paranormal" ; Bing Blog search for "paranormal"
(4) paranormal forums keyword searches http://tinyurl.com/y9akdve
(5) paranormal Google groups keyword searches
(7) paranormal Yahoo groups keyword searches
(8) wordpress.com global tag pages keyword searches http://en.wordpress.com/tag/paranormal/
(9) Keyword searches of blog directories
(10) Keyword search twitter http://search.twitter.com/
(11) Keyword search friendfeed http://friendfeed.com/search/advanced