I love the app Pudding Camera. This gives the user the opportunity to select from a range of cameras with different lens and photography functions including panorama, blur and multiple shot. The app also allows the selection of film type and as you select, the image alters through the viewfinder and thus gives the user a good understanding of the effect of each film type. Additionally, you are able to control length of shot (timer) and exposure (to a certain degree). The app is FREE :-)
I am also using Instant which is a super simple app for creating Polaroid style photos and easy to save to your camera roll. I had pondered the idea of investing in a modern day Polaroid camera but considering the cost and possible waning of my enthusiasm for said style of photography, I decided that the £2.00 app was a better bet!
Finally, for creating multiple shot images, I have discovered Pic Jointer and find this is super for making combination of photographs and the app allows you to control the size and colour of the frames and to add rounded corners too.
Of course, I also have my unbeatable digital SLR - and a telephoto lens on my wish list - but the portability and accessibility of the ipad has a lot to be said for it...