I do a lot of "iPhoneography", but don't really use any apps to complement or coordinate the work I do with my DSLR. I find that the camera (D7000) has more effective tools for metering and composition than the phone, so why not use what you paid for? The one thing that intrigued me was using the iPhone as a remote, but then I learned that it's WAY more work and far more restrictive (the camera needs to be computer or wifi connected) than simply carrying around the little wireless remote.
That said, I think there are some great iPhone apps for photography. Snapseed is the best editor I've found, and I use Camera+ in place of the default camera app as it allows focus and exposure lock and manipulation, as well as low light image stabilization (i.e. it won't shoot until you're still) and some decent post-shot filtering. TrueHDR is the best of the HDR apps I've tried (and I've tried many), and DMD is one of the easiest and most effective panoramic apps available.
