If you're looking for pragmatic guidace for securing your WCF services, look no further. The WCF Security project has been posting how-to documents and videos on its community site.
Now is the perfect time to give the team feedback. They aren't done yet and are completely willing, able, and even looking forward to apply your feedback so this can be the best resource on the 'net for WCF security questions.
If you want more details about the project, check out J.D.'s post before you head over to get the goods.