Gurobi is my favorite LP/QP/MILP solver.
In various benchmarks, it is comparable to CPLEX and is often substantially faster than open-source solvers. In many of the problems that I have been working on, it is orders of magnitude faster than GLPK and MATLAB's solver and produces solutions of higher quality/reliability.
The package currently supports LP, QP, MILP, and MIQP.
While Gurobi's commercial license is very expensive ($12000 for a single machine single user), academic users can get academic licenses (full functional) for free.