ThinkGeek: The iPhone 3GS is great but there are some limitations: floor-facing mic & inferior lens. The OWLE “iPhone Video/Audio Rig” solves these problems:
… using anodized billet aluminum, a mini boom-mic and a wide angle lens.
All four corners of the OWLE has a screw mount and comes with a 37mm lens. Other lens options include a 0.45x wide angle/macro combination one. The boom mic will help with capturing better audio compared to the one that’s in the iPhone 3GS. The price is US$129.99.