Web domain names are on the verge of extinction, take any combination of English words and chances are that the domain is already reserved.
Then internet companies tried a unique experiment called Domain Hacks - the idea is to spell the domain name instead of appending it with a .com or a .net extension.
Take for instance sites like del.icio.us and blo.gs - both are actually Domain Hacks [.us is the Top-level domain on US while .gs is for South Georgia Islands]
Finding related domains is easy with Xona.com - a domain hack search engine that calculates all the possible permutations and combinations of web domains for you.
Say you are looking for a domain like http://fictitious.com that isn't available, the alternative domains that could match are http://fictitio.us/ [.us = United States] or http://fictit.io/us/ [.io = British Indian Ocean] or http://fict.it/ious/ [.it = Italy]
And here's a complete list of top-level domains for various countries.