All I can tell you is that I did nothing when both Yahoo and MSN allowed this to happen to me. It took a few weeks and then it was gone.
Take it as a compliment – your site has made it far enough for these people to use it in their sites.
They scrape listings off search engines and use them in the site they create. Then they use a program to add different content to this site and send out tens of thousands of versions.
The search engines generally end up catching them eventually and – poof – that set of sites is gone. Now they launch tens of thousands more and the game starts all over again – but they do scrape a different set of results so someone else gets all the backlinks.
There is little you can do. If you complain to the engines they will take your complaint in consideration for their new algos, but they will not go and fix your problem at the time.
You can often recognise these sites by their URL – they will have some nonsensical basic URL – like http://www.sftgr.com and have a section added to this to make http://www.sftgr.com/blackjackrules.htm or even a subdomain.
They often solicit people by mail for links and when you follow the link path you end up finding the link on a totally different site – the actual site with the nonsensical URL.
If you type black hat seo into google you will find complete explanations.