I would like to add some information to this
Carsten is right, be careful with the term "model editor/creator" as this is commonly a tool for tweaking prefabs, assets , models for the same reason. Importing a static model is quite simple, but adding animation and connecting scripts with attributes with mesh and animation is much more complex. Thats the purpose of the upcoming Cafu Model Editor, to combine static meshes, textures, shaders and animations with different informations (attaching items, controlling sequences etc.)
For working with 3D Models and textures you will always need an external 3D software, there are many good comercial packages from Autodesk, but also quite some free ones (including full features like animation, rigging, animation and so on):
Blender (Win, Linux, Mac)
Most popular is Blender, with is the biggest open source 3D Software you can get. It is a little different in navigating and handling compared to 3dsMax or Maya but still a fully featured 3D Software for free, there will be no better.
Truespace was comercial but ended 2009 as freeware, so its having nice features like modelling, uv, rigging, animation etc, so all you need.
Seems only available on Windows, the only bad thing i guess.
http://www.caligari.com/Products/trueSp ... /Intro.asp
Wings 3D (Win,Linux,Mac)
One of my favorits in the old days, and its open source. Very powerful in modeling based on the legendary first SubDiv modeling software Nendo/Mirai
Workflow is a bit different but very flexible and powerful !
K-3D (Win, Linux)
This one is quite good for modelling and animation, yet again completly free. It gives access to poly and nurbs modeling, although you should never use nurbs objects as export (not working for almost any game engine), but you can convert it into a poly object.
Google SketchUp (Win, Mac)
Yes after all Sketchup is a good way of modelling without having to know all about modelling. Besides its quite simple and fun to use, but texturing/uv is rather rudimental/nonexistent. Still not bad for concept/prototyping. Again base version is free
A 3D Editor providing a good way of creating levels and models as it seems, its also open source with a wide userbase and plugins.
K3d Surf (Win,Linux, Mac)
Want some exotic stuff ?
K3d Surf is a surface generator based on math equations, if you can handle that its quite some fun and allows for some terrible, complex surfaces that would be quite painful to model traditional.
Maybe you find something that suits you