The mosaic filter in Photoshop can be a very useful pixelation effect, but it's restricted to turning an image into a set of squares.
This little app lets you use triangles, hexagons, bricks, cubes and other shapes, as well as adjusting size, rotation and more.
Warning: Flash Player is slowly being disabled by default in modern web browsers. If you cannot see the app below you may need to re-enable Flash in your browser.. Also, due to restrictions with Flash Player, images must be no taller or wider than 8192px, and contain no more than 16777216 pixels in total. If the app crashes, try downsizing your image first.
Questions, comments, suggestions or cool things you've used this for? Email me at dxinteractive [at] gmail [dot] com.
I'm more than happy for everyone to use this for free. If you're feeling generous then contributions are always appreciated.