I'm always on the prowl for great photo apps, so let me tell you about Fotor CameraBag (now renamed simply Fotor). It's free for a limited time, usually selling in the App Store for US$1.99.
There are a lot of iPhoneography apps that try to do everything, but many of them perform their functions poorly. Fotor CameraBag, on the other hand, does a lot of things and does them very well.
First, it has excellent HDR imaging. Take a photo from within the app, and you can make final adjustments and tweaks before you save. I put it to the test with a darkened interior room with bright morning sun in the windows and the results were excellent.
Next, for non-HDR imaging you get a variety of filters, a one-tap enhance option, frames, and something rare in an all-in-one app -- the ability to make collages.
There's also a tilt-shift option called Big Aperture that simulates the effect of a tilt-shift lens. Fotor CameraBag also includes the usual social sharing options, including Facebook, Twitter, Flickr and email.
With all of those features, there are a few annoyances. The work flow can be convoluted. You can't save directly to the camera roll of your iOS device; you save to the app's own library, and then export to the camera roll. That's just not necessary, and it should be an option you can turn off. The Color Splash tool, which allows you to selectively add or erase color, is a bit confusing. The icon to adjust brush size is simply called 'brush'. Until I clicked on it, I had no idea what it was for.
Don't let these mild criticisms put you off. Fotor CameraBag is a very powerful app, and if you want just one app for editing that includes excellent HDR, I'd give this app serious consideration. The fact that it is currently free is the icing on the cake.
The app is a 22 MB download, and works on the iPhone, iPod touch and the iPad. It requires iOS 4.3 or greater. This app has no relationship to the similarly named CameraBag, which has received positive reviews. It is an excellent filter collection, but not an image creation app.
I've got an example HDR and some screen shots in the gallery below.