Cinema 4D is a good package, but as previously mentioned, gets fairly expensive as you add more modules. One thing to think about is whether you're on the American or European side of things. C4D is developed in Germany and Europe is probably its biggest market, consequently pricing tends to the higher because of that. Not only the fact that the Euro is outpacing the Dollar but also the fact that European pricing for most software packages seems much higher than US packages. Also, if you're looking for work there are probably far fewer C4D houses in the US than in Europe. If you're working on your own though that probably doesn't matter that much.

C4d, Modo and Lightwave are all cross platform and well implemented and supported in both Windows and Mac. Maya, I believe is available for both platforms but 3DS Max is not. Max and Maya are getting way out of hand from a pricing and licensing standpoint. Autodesk as owner of most of the big packages is worth thinking about since you may find dealing with a behemoth with near monopolistic pricing power a concern.

Modo is an enthusiastic, inventive company with a great modeling and rendering tools and an excellent community. The amount of video tutorials available from the company (free and paid for) is exceptional. They have excellent, excellent, excellent training materials.

If you're into motion graphics C4D has a killer module called Mograph and a great Hair module as well.

Lightwave is in transition at the moment. It's latest version 9.6 is very stable and an excellent value for the money. The are in the process of developing a new version of Lightwave called HardCore which will probably take a year or so to get up to speed with their current 9.6 version but is a complete overhaul of their core programming base. Probably trying to emulate Modo in some respects. Looks like they are going to a model which will require annual updates similar to Maya and Max but probably not as pricey. Their pricing has been way too low to sustain them in recent years and I can understand the need to raise prices and develop a more predictable, sustainable revenue base.

I'm just a hobbyist so take what I say with a grain of salt. But over the years I have owned each of these programs and currently have Modo, Lightwave and C4D. Any of these are a great addition to MOI.

Good luck.