GAUSSIAN (www.gaussian.com) for molecules or clusters models
CRYSTAL (www.crystal.unito.it) for periodic calculations with localized orbitals
VASP (http://cms.mpi.univie.ac.at/vasp/) for periodic calculations with plane waves
QUANTUM-ESPRESSO (www.quantum-espresso.org) for periodic calculations with plane waves
The Quantum Chemistry group at the University of Milan-Bicocca has at disposal several Linux clusters with in total 15 nodes: 14 nodes with each 64 AMD Opteron Processors, 1 node with 32 64 AMD Opteron Processors, and some smaller workstations.