I love these iPhone apps...
Hipstamatic:
It's designed to be washed out and vintage in style, a bit like an old Polaroid. There are all sorts of combinations of lenses, films and flash modes.
ShakeIt:
A similar application, attempting to create a vintage look. On this one you can only change the frame. The best bit is watching it develop slowly, just like a Polaroid! You can shake it to speed things up, but I think that just spoils the fun!
(Maggie O'Farrell's book is wonderful, by the way...)