There is quite a few broad topics suggested for the LHC[1], and even right now there are 3 other experiments running on it[2]. (ATLAS is the Higg's boson experiment, although it isn't just looking for the Higg's boson.)
Figure out how the heck the Higgs boson actually behaves, for starters (they just found it). But my understanding is the LHC is not a single-purpose tool. You can observe a variety of particles at a variety of energies.