The American Museum of Natural History has posted an online exhibit called Picturing the Museum. Included are a series of archival photos showing old exhibits at their museum, the most interesting (to me, anyway) being a bunch of behind-the-scenes photos showing the staff putting together exhibits. The photos are all over the map, but in general are a fascinating look at the making of great exhibits. Some of the photos are picturesque, like this shot of "Sister and Sammy Keith collecting tadpoles for Trailside Museum" from 1931:
There are also old-timey pictures like this one, entitled "Museum staff assembling bones of dinosaur fore limb for exhibition," and taken in 1916 (check out the mustaches on these dudes):
But many are downright creepy, like this one entitled "Preparation of Millipede model, Preparation Department" from 1957:
View tons more of the Exhibition Preparation photos (twelve pages in all!), or check out the entire collection, which includes sections on Dioramas, Education, and Exhibitions. Another option is to check out this nice article which selects some favorite images and gives some context.