In this talk I will discuss quantum states of bosonic lattice systems and present benchmark results, based on quantum Monte Carlo simulations, for phase diagrams. These systems provide unique opportunities to explore interesting problems in strongly correlated physics, providing a wide variety of novel ground state phases (e.g. supersolids, paired phases, Bose glass) and phase transitions, with the possibility of comparison with experiments. I will be focusing on the following two systems: i) bosons in a disordered square lattice potential ii) bosons interacting via dipolar interactions in a bilayer geometry. I will present the ground state phase diagram of both systems as well as finite temperature results.