The electromagnetic force (specifically, the Coulomb interaction) is 1/r^2. The strong force is actually effectively constant at long ranges, since it becomes energetically favorable to create an antiquark/quark pair. The residual strong force is exp(-r)/r. The weak nuclear force is exp(-r)/r^2 (or exp(-r)/r? I can't really tell with the links on hand--I just know for sure there's an exp(-r) term in it). Gravity being 1/r wouldn't be a surprise given the other known forces.