The Tech Report has compared seven 600W to 800W power supplies from BFG Tech, Enermax, ePower, Mushkin, OCZ, Thermaltake and Zalman.
We've limited the wattage range of this round-up to between 600 and 800W because that seems to cover the meat of the enthusiast PSU market. Enthusiast rigs that pull anywhere close to 600W—let alone 800W—may be rare in the wild, but with CrossFire and SLI multi-GPU schemes becoming more popular and graphics chip makers pushing for new PCI Express standards that support higher wattages, we think it's prudent to have a reserve of untapped power. We also want to have the right mix of connectors available for future upgrades, and this class of PSU tends to have them. This wattage range is well beyond the capabilities of budget generic models, which is why you won't find one of those included in the mix. Generic PSUs, it seems, aren't generally available above 500W.
Check it out over here. The best unit was the PC Power & Cooling Silencer 750W, this is the quietest PSU in its class with great power delivery and efficiency. Also recommended are the BFG Tech ES-800 800W, OCZ EliteXStream 800W and Zalman ZM-750HP 750W.