Draw Something is a great android app that has taken the market (or should that be "Play") by storm. After its release it has almost shot to the top of the market, and for good reason. Draw Something is ultimately, an on-line, quasi competitive version of Pictionary. Players take it in turn to draw pictures, whilst the other players try and guess what the image is.
Images are rated in difficulty from 1 - 3 coins (with three coins being the most difficult), and the risk of drawing a more difficult image can pay off with higher points. Get it wrong though, and the "partnership" goes back to zero. At the moment, the highest winning streak I have obtained is 13, but many games finish after four or five goes.
In short, get Draw Something, get a few friends on board (or even a few randoms) and you will be guaranteed to sink many hours into your device!
In the words of the developer:
The most popular social drawing and guessing game on Android!