Poser 8 ($250, buy-only) is an industry standard application that allows for the creation, importing, and manipulation of 3D figures, usually human beings. These figures can be modified, posed and given clothing, hair, and accessories to an extreme degree. Then, these scenes can be imported into Anime Studio Pro, 3ds Max, or other applications and used further. Or, the anatomy and light source of the posed figure can be studied for a 2D paper-and-pencil artist, in the same way he or she would manipulate a plastic figure or clay model.
From that paragraph alone, you might intuit that Poser is extraordinarily versatile, and you'd be right. Many webcomics, such as the extraordinary Dreamland Chronicles, are created from Poser figures alone. Poser is also often used as a starting point for 3D characters found in many videogames.
Poser is easy to use for someone completely unfamilar with graphics software. It's fun to just fire up one of the eight example figures and manipulate the heck out of it with the included tools. One of the most fun things to do is zoom in on the face and adjust each level of facial features. You can imagine criminologists using this in lieu of a sketch to track down bad guys. Once you become more familiar with the software, you can even do crazy things like adding horns and realistic scales to characters. The sky's the limit, really.
The one drawback to Poser is that there's no demo at all for version 8. Your only option is to buy the $250 software blind. Going by reviews is your only option, and this particular review recommends Poser highly.
If you're looking for a lot of example content from which to build, you can find many paid Poser objects and scenes at Smith Micro's Content Paradise site. If you don't wish to pay past the software's high price tag, a Google search or a visit to unofficial Poser site Poserpedia will garner you thousands of free choices.
Whether using the 3D figure as reference, making 3D comics, or importing into other software and going from there, Poser is the gold standard for 3D figure reference.