Apophysis 3D. Proof that you don't always have to use the software for dramatic 3D images, but can still create some incredible designs.
I don't think I will ever tire of the great infinity of designs that are possible using the Julia variation. Added to some of the amazing plug-ins that the developer community has added to Apophysis, and you can create a mandala that allows you to meditate for hours.
Downloaded size is 4800x3600. Printed, 48 inches by 36 inches makes for a very dramatic wall.