LiveGraphics3D
http://www.carloangiuli.com/graphics
LiveGraphics3D is an awesome Java applet that allows real-time rotation of 3D objects in a web browser. I have written this Perl/HTML wrapper to make it usable for anyone, not just people who can figure out how to run Java classes. A much better explanation and a whole bunch of graphics can be found at the URL above.
If you have some graph you’re just dying to see, but you don’t have Mathematica, you can leave a comment here and I’ll put it up for you. I’m nice like that.