Well, this may or may not be useful. Because it messes with the shape a bit, it might be a bit difficult to implement. By adding and modifying some warp effects to a 3D box object with a water texture, you can create a sort of 3D water effect. If the box object isn't rotating, it looks more like a awesome 2D water effect.
<img src="http://i55.tinypic.com/122kvgh.png" border="0" />
<img src="http://i54.tinypic.com/2rqegzb.png" border="0" />
There's two caps, one with the 3D-ish effect and one with the 2D effect that could be used in a platformer or something.