My DSLR iPhone apps include:
PhotoBuddy - It's a multi-purpose tool, but I typically only use the DoF calculator. Supposedly some of the functions don't work as well, but I haven't tried them out.
Pocket Light Meter - Exactly what it sounds like; a light meter app. And it actually works quite well, too.
I've tested it next to a camera and the exposure readings are pretty accurate. I'd say that it's probably accurate about 80-90% of the time, and otherwise it's within a 1/2 stop.
Easy Release - Basically your model release form on your phone. Pretty nifty little app, though using it on the iPad is obviously more practical.
Pics - a pretty simple little portfolio tool. There are others out there that are a little more user-friendly, but I like the operation of this one. Works well on the iPhone, but again, I prefer using it on the iPad better.
I have DSLR.Bot, but haven't attempted to use it yet. Tried building my own IR device, but I failed. Might buy one later.
iPhone camera apps I use:
ColorSplash - fun little app for selective color images
Juxtaposer - Figure it out.
PS Express - Mobile Photoshop. Great little tool, though pretty limited. I have used it quite a lot, though.
There are other apps I have but almost never use like timers and sound triggers for the iPhone camera.
Also, though not a smartphone app, I have to say that Photogene on the iPad is a great mobile RAW editor tool. Haven't really used it a lot yet (I just got it) but so far I like it.