ArchiveGrid (http://archivegrid.org) brings thousands of archives worldwide together, making it easier to find primary source collections--information that's otherwise very hard to track down.
ArchiveGrid is freely accessible through May 31st, and they're getting the word out so that as many researchers can take advantage of this open access period as possible. If additional grants funds or sponsorship are obtained, ArchiveGrid will remain free of charge; otherwise subscriptions will be available for institutions and individuals alike. For now, though, get in there and dig around. If something you seek resides, say, with the National Society of the Colonial Dames of America in the State of Minnesota, rest assured that ArchiveGrid will find it. Hey, you never know.