The older Thermaltake Toughpowers were great, but I had heard that their quality has dropped in the past couple of years (they've even gone to single +12V rails...). I love the modularity of these units, though. Around 800w is good for a multi-GPU system. Always look at the power requirements of your components, though. There are configurators around that will calculate power requirements based on the components you input and suggest a PSU rating based on that. A good baseline is to get a PSU with a maximum wattage of twice your required power. Also, always look for units with at least an 80% efficiency rating. You can find such units through the
80 Plus Program.