Easy Black And White is a fast and free app to convert any image into a two color black and white image. It features a convenient sliding scale threshold for conversion, and the ability to select your two colors (they don’t have to be black and white!). This is handy for creating artistic renderings, two-color icons, game art, and more!
You can download it from the Android Market here.
Update 4/2012 This is now open source and hosted on GitHub. Check it out at my GitHub page.