Simply B&W is a relatively new iPhone app. It is a very simple app where you can convert a photo to black and white and then apply a color filter. You can also adjust the brightness and contrast of the image.
The beauty of this app is the simplicity. You just choose from one of the five color filters, and then tweak brightness/contrast.
Changing the color filter on a B&W image can have significant impact. The app gives you helpful hints about what each filter does as you select it. I applied each filter to a snapshot I took the other night at a local pub. You can see how the images get a different look when the different filters are applied (click to see larger version).
Simply B&W is currently $0.99 (download on iTunes) which is worth it. You can achieve the same effects with more complex apps, but one tap simplicity is often the best approach.
And for those that are quick, here are six promo codes. Grab one while you can!