Forum Moderators: not2easy
When in doubt, check sites that can afford expensive attorneys and see what they do. Be aware, of course, that doing so isn't a substitute for having your own attorney who knows your business, your regional laws, etc.
That, $30, and a CD sent in the mail is a very good idea if your site is worth anything. If accepted within 3 months of publication, it also entitles you to statutory damages as well as actual damages if your copyright is infringed, as well as serving as fairly absolute proof of originality.
According to the U.S. Copyright Office [copyright.gov], registration is required before an infringement suit may be brought in a U.S. court for works of U.S. origin.
Jim