* Macromedia – Ahem, Adobe – Flash (obviously)
* Moho by Lost Marble (Inverse Kinematics in 2D!)
* Plastic Animation Paper (not really for character work, but great nevertheless!)
* Any of the main 3D apps (obviously). Personlly I recommend XSI, it is especially powerful for character work and has some nice built-in models, rigs and animations (check out the Net View).
* Poser (well, not really, but it has some nifty built-in walk and run cycles you can render flat and use, say, in AE)
Good luck,
AA