...And what you can afford. Maya and Lightwave (not Lightware) each run for $2000 and $2500, respectively, while Cinema 4D is in the range of $400 or so. Also, there is Electric Image's Universe, plus other more specialized programs like Bryce (landscapes), Poser (people), and AutoCAD (architecture).
For hardware requirements, an iBook will suit you fine, especially if you have a reasonable amount of VRAM. Most of these programs do okay in software rendering modes, but the thing that helps is lots of processor power and lots of RAM. All that you will miss is rendering time.