One of the best black and white apps for the iPhone is now available for free from the AppStore.
Vint B&W [AppStore Link] from Erik Pettersson offers the best tonal range of any black and white app currently available for the iPhone (see sample below), however unlike other apps in this category, you can only take photos with it, converting them to black and white as they are saved.
The app does however support full res, and tap-to-focus on the iPhone 3GS, and for free is a bargain not to be missed.
In addition to Vint B&W being free, Erik's other apps, Vint Red, Vint Green and Vint Shift are also free.
Note: I am not sure why, but at time of writing, these apps appear to have been removed from the UK AppStore.
UPDATE: I have contacted the developer of this app regarding its absence from the UK and European AppStores, and he hopes to have it back by the end of May. As soon as I have more info on the return of this app, i will post it here on the blog.