If you like to do any 3D modelling or animation, Pixar's in-house software that's been used for movies like Toy Story, Cars, and recent films like Guardians of the Galaxy is now completely free to download and use.
RenderMan is used by the big time studios to create photo-realistic lighting in CG scenes, and has been used by Pixar to render every one of its animated features. You can download it for free and use it as much as you want, but the one catch is that this is a non-commercial licence -- you'd have to pay for one of those you're looking to make money off of your creation.
It's important to note that RenderMan is not a 3D modelling application like Maya or KATANA, so you'll still need to make some 3D models or animations to render. Of course, you can always grab the free trial of Maya or a free copy for students and teachers to get started. You can download RenderMan at the link below.