don't forget the yang-mills mass gap and the navier-stokes initial value problem, both clay millennium problems and both rather important. Well the yang-mills one is probably more important, this list is a bit m-theory biased.
I think the m is originally for membrane, not "magic" but apparently its open to interpretation.
The way those problems are posed, by the Clay Institute, they're more math problems than physics problems. Check out the price lectures on their site to see what I mean.
I think the m is originally for membrane, not "magic" but apparently its open to interpretation.