I've been using the Nikon 10.5mm DX f/2.8 for a while now, and find it really useful. It's great for different-perspective shots, such as huge, cloud-filled scenics or warped sports shots. The only downside is some visible chromatic abberations (purple and green edges in high-contrast areas) in the edges of the frame. Other than that, it's well worth the uh.... five hundred bucks.