I've put links to my artwork in my signature (click on "My Imgur Profile" and "My Gallery"). There you'll see my artwork (my newest and best piece is my current signature pic).
As for tips, I'd say learn to use layers and the text tool. Also try to use C4Ds more so it looks like you did more than just add text to an image. A good site for renders (PNG images that are cool and free to use) is renderat.com. I use GIMP so the program might run differently than with what you use, unless you use GIMP as well.