if you're modelling for warcraft 3, you can pretty much only use 3dsmax, but that's not free.
Most modelling tools are commercial and expensive, simply because they require so much time and effort to make it would be insane not to charge for them.
I can give you the names of some products though, like Milkshape, Maya, Lightwave, Poser, Bryce, and Cinema 4D.
edit: oh wait, I believe GMax is free, and I hear rumours from time to time that gmax models might work in warcraft 3, but I haven't yet heard anything in concrete.