blocky scaling

[Vincent Rosati]

Go into Photoshop-Edit/Preferences/General:Image Interpolation.. and set it to >Nearest Neighbor<. This option will also be available within a Scaling dialogue. Nearest Neighbor interpolation will give you a nice blocky look when resizing.

[Mike Gondek]

Also check out the filter >> pixelate >> mosaic if you are looking to create a pixelated look