I've been working on a method for real time lighting on pixel art. I've put some videos up on YouTube. Latest one here
I haven't written up my method yet as I'm still finishing up some details, but you can see the idea. I do it by offline rendering various normal, material and occlusion maps into my sprite sheet alongside the diffuse colour, then doing similar to a 3D deferred renderer but using the 2D sprites to populate the geometry buffer. It supports dynamic point lights and directional lights so far.
It's a bit similar to the Gamasutra article I guess (though that article hadn't come out when I started working on it.)