I bought my iPhone 3G for many reasons. I liked the idea of consolidating many devices into one, but really, I bought it to take pictures. I heard the camera was better than decent and the email capabilities would help me send photos to Flickr.
Then I discovered the App store and my previous notions on what I would use the device for went right out the window.
I have ten pages of apps on my phone now: two for highly used apps, two for games, two for photo apps, and the rest for random apps I somewhat use.
When it comes to photography, I found these to be my favorite and most used apps:
Hipstamatic is a beautiful application - a little pricey after you download all the additional packs (as apps go, anyway) - but beautiful none-the-less. Experimenting with the different lenses, films, and flashes makes taking a photo an interesting experience. I feel like a little kid again, running around with a new toy camera. The results are O.K. The resolution isn't that high and there are lots of artifacts from the processing. I honestly use it for the fun factor and if an update improves the resolution, wonderful - I'll still use the crap out of this app!
Photogene, Photoforge, and Photoshop are my editors of choice, although I spend more time in Photogene.
Camera App (the stock one) is very important to me. It's fast, it's simple - it just works. Yea, it could use a grid or a timer, but you know what? It is the fasted app to save photos. I use it so much, that the shortcut (double home button) is tied to the camera as well as it taking up residence in the quick launch area.
LOFI, Polarize, Edwin little, Best Camera, and Mill Colour all have great filters for my images. I'd have to say that I lean more towards the "lofi" stuff but I use all of these depending on how I'm feeling. I really like LOFI's black and white filter, but Edwin little has some sweet borders.
I'll keep this updated as this page on my phone changes. Also, I am starting to update the photoblog more often as well.