If you are a casual photographer and primarily use your iPhone 4 or 4s you should check out the olloclip. I was introduced to it at this year’s Macworld and am quite pleased with it.
This tiny attachment includes fisheye, wide-angle and macro lens. It simply slides over the camera lens on your phone. The MSRP is UD$69.99. The package includes a carry bag that doubles as a lens cloth. Home page is: http://olloclip.com/index.html
I like it because it is so very easy to use and I get clean pictures from it. Someone asked me about the pixels, and I assume the pixels are whatever is available through the camera. The olloclip is not going to affect that one way or the other.
Following are two quick snapshots I made, one with my camera without the attachment and one using the olloclip on wide-angle. It is easy to see what a difference it made.