Buying an expired domain name that has been used previously to host a site related to your topic is becoming a a popular way to get cheap targeted traffic. People allow domain registrations to expire and become deleted for different reasons, and may not realise the value they have.
How to find expired and deleted domain names and websites
Deleted and expired domain names can be found at many domain registrars, however some charge for the service. Some of the sites I recommend are:
pool.com
What to look for in an expired or deleted domain name
Before buying a deleted domain name check out the following:
Is the domain still listed at the major directories?
Being listed in the major directories is important not just because of the traffic that they provide but because they give a boost to your domains ranking at google and other major search engines.
DMOZ Submission and acceptance at DMOZ directory can take time, and may be impossible depending on the nature and content of your site.
Yahoo! If the domain is listed at Yahoo’s directory it can save you the $299 cost of submission for a commercial site, or a serious wait for listing of a non-commercial site.
Does the domain have incoming links?
This can be checked at google using a link: search, for example use link:pilkster.com
What was the domain previously?
Checkout the previous life of the the domain at the wayback machine, archive.org’s cache of the web. Using the wayback machine can also reveal the identity of the domain names previous owner.