Gimp is really good considering it's free when you run out of the photoshop trial or don't want to pay for it. Of course tutorials for gimp are a little harder to find, but I'd say it's worth a shot since it's free. You can get it here:
http://www.gimp.org/ I don't think you can do the Cinema4D stuff with it though.
Edit: By the way you can get a lot of renders from here:
http://planetrenders.net/ and if you join the forums, there's a lot of good free tutorials. After you get more active you get access to stocks, brushes, and other free sources.
http://www.dafont.com/ is a good site for text also. Good luck!