X-bit Labs has reviewed 14 power supply units with a capacity of over 1000W, you can check out their roundup over here. The best unit is the Enermax Revolution 85+ ERV1050EWT, followed by the OCZ Z series Z1000M.
First of all, it is the Enermax Revolution 85+ ERV1050EWT. Enermax has promised a power supply with best possible specs and seems to have delivered it. This is a quiet, high-wattage, stable PSU with a generous selection of connectors and excellent efficiency. Enermax is the best product in this review.
The Revolution series used to be the only one to boast 90% and higher efficiency. Now it has got an opponent in this respect. The OCZ Z series Z1000M is a high-quality, compact and rather quiet PSU that has an efficiency of 91.7%. It offers a good selection of cables, too, providing 12 connectors for SATA drives and three pairs of connectors for graphics cards.