It really depends on how much you want to spend on it. 3D modelers go anywhere for thousands to free. If you have around $600, Rhino seems to be the modeler of choice. Another good one but a bit more expensive is 3D Studio Max. Speaking of freeware, if you have anim8or, that's a good place to get your feet wet since it exports .obj files. It's not really going to give you the tools to do human figures but it will let you get a start with simpler meshes.