Good modeling software for new assets

[Gilligan's Hell]

You could try and use:

Blender (Free, but can't rig enemies.)
Maya 2011 (Unless you're trying to rig a monster, any version is fine. You can choose to pay it of use the Student version.)
3DS Max (Pay, but good to rig enemies.)

Each program has it's ups and downs, but it's entirely up to you.

I've got blender and I'm currently downloading Maya 2011 student version. I'll test both to see how good they are.