I'm using pcpartpicker and it says that my estimated wattage is 361W. http://pcpartpicker.com/p/E2Hh. That's my build if you need to see it. I'm just wondering what PSU I should buy, in terms of watts.
For a system using a single GeForce GTX 670 graphics card NVIDIA specifies a minimum of a 500 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 30 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most important factor.
The PSUs recommended by @djangoringo meet the requirements.
A single GTX 670 will max out a 173W. That requires 14.4A on the +12V rail(s). I would feel comfortable with a good quality 550W+ PSU for your system as a minimum. The above mentioned brands are good choices, as are Corsair.