I am completely, hopelessly, wonderfully addicted to the Hipstamatic app on my iPhone. Best $1.99 I've spent on apps yet.
It's got different lenses, film, and flashs' you can use in a million different mix and match ways.
But my favorite combination is the John S lens and Ina 1969 film, no flash.
You should see the hundreds of other photos I have on my phone that I haven't posted (yet!).
It is by far my most used thing on my phone now! (that and Bejeweled 2)