Some of the most outstanding problems of physics lie in the understanding of the dark sector of the universe, in particular dark energy, neutrinos, and inflation. The dark energy and neutrinos are correlated through their effects on distances and the clustering of matter. I will review the present state of surveys sensitive to the effects of dark energy and neutrino mass. I will then forecast how well the present dark energy density and its equation of state along with the sum of neutrino masses may be constrained using multiple probes that are sensitive to the growth of structure and expansion history, in the form of weak lensing tomography, galaxy tomography, supernovae, and the cosmic microwave background. I will include all cross-correlations between these different probes and allow for non-negligible dark energy at early times (motivated by the coincidence problem) in spatially flat and non-flat cosmological models. In the latter portion of the talk, I will discuss a novel method to constrain non-Gaussianity of the primordial density perturbations by its impact on the ionization power spectrum from 21 cm emission during the epoch of reionization. I will show that 21 cm experiments in the near future may constrain inflationary models via primordial non-Gaussianity to the same precision as expected from Planck.