Blender's the biggest and (probably) most popular free 3D app, but the user interface sits somewhere between the cockpit of a 747 and a space shuttle, complexity-wise. My preferred 3D app is 3D Studio Max, but that's about as far from free as it's posible to be - I'm lucky in that I got an educational licence from when I was at university and "forgot" to uninstall it when I left there. Hmmm, must get around to that one day.