A while back an add-on called Cubify was released. It took and image and converted it into basically a height map. It was very slow once the image got above the size of about 32x32 though. CubeSter has the same basic ability, but runs about 1,600 times faster, meaning images with over 450,000 blocks can be generated in about 30 seconds.
- Image sequences can be used
- Audio files can be used
- Blender Internal can be used
- Better time estimation
Side note: if using a laptop, try plugging it in. In my experience this can decrease the time it takes to generate the mesh by around 140%.
Block Based Mesh (46,656 blocks in 2.71 seconds)
Plane Based Mesh (192,600 points in 1.92 seconds)