Some good tricks with curves

Source

This cool video shows how to use a posterized gradient to make a set of tonal rectangles.

1. Add a horizontal (O°) gradient adjustment layer running from one tonality or color to another.
2. Add a posterize adjustment layer. It’s property panel lets you set the number of separate tones/colors in the gradient. An odd number guarantees 50% grey somewhere.
3. Clip the posterize layer to the gradient layer.

This is really cool.

More can be found here, including a downloadable action.