FiLMiC Pro is a US$2.99 app that boosts your iPhone video as close to pro quality as it can get. The app allows selectable resolutions (1280x720, 640x480, 480x360) and a variety of frame rates like 30fps, 24fps all the way down to 1fps.
There are a number of great features to get you started. You can focus-lock on any point with your finger and lock the exposure the same way. This prevents the camera automation from "hunting" for the right settings. FiLMiC also offers color bars and a personalized slate.
Exposure settings range from the whole frame to a spot sample. A handy audio level meter is superimposed over the screen, and framing guides for 4:3, 16:9 and 2.35:1 aspect ratios keep on you track.
Movies can be saved to your camera roll, DropBox, YouTube, Vimeo, Facebook or Tumblr. I tried shooting some video and found the experience far better than the stock Camera app. Of course FiLMiC can't make the iPhone camera hardware any better than it is, but it surely brings in features that will push the camera on the iPhone to the limit. I was surprised how good the video looked.
If you are serious about video on your iPhone, this is the app to get. It's a steal at $2.99; I would have expected to pay more.
Check out a great, pro-looking sample video here. This video was shot at 24fps; expensive equipment was used (a Steadicam Smoothee & a GorillaPod) and some track was laid for moving the camera. Not a typical handheld job, but impressive.
FiLMiC requires iOS4.1 or later, and works on a 3GS, iPhone 4, iPod touch (4th generation) and the 2nd generation iPad. Video quality and some features will vary depending on the iOS device you use.
Check the galleries to see the range of video options you can choose.