You can download the latest Autodesk software for free if you're a current student, staff member at an educational institution or qualify for the Autodesk Assistance Program*. All of the software is fully functional, but unsuitable for commercial work (renders are embedded with banners). The titles available for download include (but are not limited to) 3ds Max, Maya, AutoCAD, Mudbox, MotionBuilder and Softimage.
Visit the Autodesk download center at http://students.autodesk.com/?nd=download_center.
* Autodesk Assistance Program participant - either a veteran or unemployed individual who has (a) previously worked in the architecture, engineering, design or manufacturing industries, has completed the online registration for the Autodesk Assistance Program, and upon request by Autodesk is able to provide proof of eligibility for that program.