Crank Brothers
Lightest are the basic eggbeaters - especially the ridiculously expensive triple ti version
Mud clearance is also the best there is. Downsides are lack of foot support (you need a fairly stiff soled shoe) and no platform for riding unclipped.
The Candy SL addresses most of the downsides of the basic eggbeater. I ran these for a while and was fairly impressed. The platform provides better foot support, but is too small to be of much use when unclipped. The outer cartridge bearings failed within 6 months, but were very easy and fairly inexpensive to replace (£9 for a full service kit). Perhaps it was my fault for not re-greasing them regularly. They are also still very light compared to Shimano equivalents and shift mud more effectively.
I'm now using the bigger platformed Mallets (Mag version) which are superb. They are billed as a downhill pedal, but I think they are the ultimate trail pedal. They are still pretty light, clear mud well and can be ridden clipped or unclipped as you feel like. I always ride clipped, but it's nice to have a decent platform to use when setting off in awkward places etc.
It's worth mentioning that the clip system on all eggbeaters is great - much better than Shimano offerings. Very simple and well engineered concept.