Dot is a iPhone camera attachment that, in the words of its creators is: "a stylish, durable, and downright pocketable 360º (panoramic) lens attachment and app for the iPhone 4. It lets your iPhone capture immersive, fully navigable, panoramic video in real-time--and share with friends on your phone, as well as on Facebook and Twitter, or streamed online using our awesome panoramic video web platform and player.
This one is actively in the works, as their Kickstarter campaign has been more than funded.
Leica i9 for iPhone 4:
This one's just a concept (as yet), but if made would allow for the Leica i9's housing to be snapped onto the front of the iPhone 4, allowing for the use of the Leica's lens, as well as lending Leica's quality looks, to your previously regular-functioning and regular-looking iPhone. (Via HUH Magazine, this concept is being developed by Black DA.)