Teachtopia's Guide to Natural History Museums with Virtual Tours and Online Field Trips
National Museum of Natural History This Washington DC museum is part of the Smithsonian institute. Their virtual galleries are both of current and past exhibits.
National History Museum (London) This museum has multiple virtual tours to visit.
North Caroline Museum of Natural History has several virtual tours.
LA County's Natural History Museum. This Los Angeles Museum has a Dino Hall has a virtual online exhibit that is worth seeing.
American Museum of Natural History in New York City has several online exhibits.