I'm aware of quite a few sites out there (e.g. morphobrowser, morphosource, nespos, evans) but I'm always looking for more.
In particular, I'm looking for ones that have CT scans high quality enough to do research with...i.e. the Digital Morphology Museum, KUPRI has a TON of amazing primate CT scans for free download. However, they're not particularly high quality, making it difficult to use for anything other than gross geometric measurements and/or teaching.