A Stanford student has tried to capture 4D by being able to take a picture that allows a person to focus in at different depths. Of course, this is really just 3D, but the student has created (or perhaps re-created) an interesting 3D effect. As Digg user bivouac points out, "Wouldn't four dimensional photography be video?" I agree that's one representation of 4D.
As I've said before in An Introduction to the fascinating patterns of Visual Math, I just don't think it's possible to show 4D in a still 3D setting. Artists have tried to capture 4D by forcing people to use their imagination. But the results are inevitably inaccurate.
My favorite representation of n-dimensional space would be the hypercube.