I am a big fan of Mental Ray and have been using it for years now. It was accessible and there were tons of resources. I am still a big fan of it, but it was also the only render engine I had access to and honestly all I knew. RenderMan has just been released free for educators to work with. Check it out and get rendering; I will. - Cornell
Pixar's RenderMan for Maya 3.0 (Instructor License)
JourneyEd Item No: 100965128
Manufacturer Item No: JEM-IE-RFM30-NL
Pixar's RenderMan Studio 2.0 with Embedded Renderer (Instructor License)
JourneyEd Item No: 100965135
Manufacturer Item No: JEM-IE-RMS20-RER-NL

Pixar's RenderMan Pro Server 15 (Instructor License)
JourneyEd Item No: 100973954
Manufacturer Item No: JEM-IE-RPS15-NL
Pixar's RenderMan Classroom Kit (Educators/Staff only)
JourneyEd Item No: 100965320
Manufacturer Item No: CLASSROOMKIT
http://www.journeyed.com/dept/Brands/Pixar/RenderMan%20for%20Instructors/291839?qk_srch=JEM_PIXAR_INSTRUCTOR