Well maybe this sounds a tad bit stubborn but personally I''d use a 3D API without mipmapping or anything of that sort. Throw in some vertex lighting on your Quads and VOILA! Lighting! Plus you get hardware alpha, rotation, scaling, etc to boot. Of course, you have to make sure you keep your coordinates VERY accurate. Nothing looks worse than cracks in 2D.

That''s not actually what he asked though...

I''ve been thinking about this myself, and I''ve come up with a few ideas.

The first would be a kind of light mapping where the offset of the pixel is used as an index into a light texture, and then blend the intensity with the base pixel. It''s actually very similar to bump mapping but without the bump

The other idea was a per-"vertex" method where each pixel is gradient shaded according to a brightness value at the corners of the bitmap.
I''m sure all of the standard lighting models could be applied to a 2D surface, like we used to do to polygons before hardware cards came along

You wouldn''t want to dynamically light a whole tile map in real-time, but with some static pre-lighting and then a few dynamic lights it should run OK.

Coloured lights are almost exactly the same but instead of using a byte value for illumination you use a colour value, and multiply each colour channel of the image by the matching channel of the lightmap. Incidentally this is totally free (over the non-coloured) if you use MMX instructions to do your pixel operations.

I''ve written a 2D bumpmap routine with coloured lightmaps and that runs pretty fast, I''m working on a tile engine at the moment that I can add lighting to.

The Intel Developer site at developer.intel.com has the basic
docs, and I think there''s an article on mmx alpha blending here on gamedev. I''m assuming you know assembler, it''s the only way to use mmx directly AFAIK.