I was at one time working on a plan to get three of the iMac G3's and arrange them in a triangular pattern on my floor, and make them into a coffee table by somehow attaching a large slab of glass on top of them. I had two already and just needed to find the money to get one more, but I was forced to get rid of them.
Personal story aside I think furniture that rejects sharp angles as much as possible, and instead uses smooth curving would be a good choice to go with the "egg" shape of the iMac.

Sorta like the "futuristic" look furniture had back in the 60's/70's. The color schemes of that era probably would fit the iMac range pretty well too, actually.