iOS: We've seen manual camera apps for iOS before, but Reuk offers a slightly different take on the idea. It includes a full set of manual controls, but it's also surprisingly easy to use.
With Reuk, you can toggle flash settings, alter the shutter speed, ISO, white balance and focus, and set a timer. You can then lock in those settings so you can easily adjust others to get a real-time view of how your picture will turn out. Most importantly, it's fast, and adjustments are intuitive enough that you don't need to be a photography pro to understand how do everything.
Reuk ($1.29) [iTunes App Store]