If you're looking to build out your domain portfolio with some recently expired domains, make sure to check out DeletedLive.com. The service enables users to search for domains by keyword and returns a list of domains that have already expired or are expiring that you can scoop up on the cheap. DeletedLive does a nice job of displaying the Google PageRank of these sites, along with its expiry date, the Google links, a link to the Archive.org Wayback machine and quick access to the domains Whois information. I found a few domains while testing out the service - see if you can buy them before me.