The Federal Registry for Educational Excellence (FREE) is a collection of digital teaching and learning resources created and maintained by the federal government and public and private organizations. If you are looking for lesson suggestions or resources to spruce up existing ones, check FREE.
FREE offers resources in language arts, math, science, social studies and health/PE. The site also allows searching by standard for Common Core math, geography and science. Teachers can limit the search by clicking the Federal Resources Only box, but that eliminates the vast majority of quality results.
FREE was launched in 1997, and the new version is currently in Beta. It is powered by the Learning Registry, which collects and shares learning resources that are available online (including OER Commons and Annenberg Media). It also accesses information from over 100 federal agencies including the Holocaust Memorial Museum, the House of Representatives, the Census Bureau, the U.S. Geological Survey, and the National Park Service. Remember that any resource provided by a government agencey is copyright-friendly (except that "security related" stuff) as long as it's properly cited.
A search on the Holocaust came up with 72 results, only five of which contained significant material. Those were from the Holocaust Memorial Museum and Library of Congress. The good news is that the information provided in the search results was sufficient to determine what site was good and what may be a mere mention of the search term.
Be sure to click About Free at the bottom of the home page. You will see the list of federal agencies connected to the site. Be aware though, clicking on, say, the National Gallery of Art, will not bring you to that site or to resources provided by that site. It does show you the vast, eclectic mix of resources available that may be associated with art (astronomy to jazz to deserts). Fun to check out!