Tetris has come to us in many forms since its release in 1984, some more interesting than others, but few manage to combine functionality with fun as well as this stackable Tetris LED lamp, which only lights up pieces that are connected to each other.
Available for $US39.99 on ThinkGeek (not including shipping), the light comes with seven pieces -- one of each type -- though if you'd like to construct some sort of illuminated Tetris mega-sculpture, you can grab multiple packs and combine them.
The dimensions of course change depending on how you put them together, but the typical stacked configuration sees it measuring 17.78 x 10.16 x 2.54cm. If for some reason you can't imagine what this would look like, here's a helpful video.
It's a shame the pieces can't light themselves individually. It'd be cool if you needed a small light for something, say working on the innards of your PC, and you could just grab a piece and use it as temporary illumination. Well, there's an idea for version two.