I just discovered this gem: Blocky - Free Online Game from Shockwave

Blocky - you need to select squares from a set of blocks with the same colour blocks in the corners, so for example all red blocks in the corners but with any colour in the other squares.

Once you select a square you "de-activate" those blocks, you need to "de-activate" all the blocks in the grid to advance to the next level which will contain more blocks and more colours.

Its a bit tricky at first, but quite addictive...

Have Fun!