What is the best power supply for a pc thats mainly used for gaming. ?
Ok... You question is so vague I can't really tell you anything. First of all there is not such generic PSU. A PSU is chosen based on the hardware that is in the box. So unless you tell us more about your hardware no one here can't give you a decent response.
your main title is best vid card and you ask for power supply???
video card, get atleast an ati 4870 1 gig gddr5, and as for power supply get this one. http://www.coolermaster-usa.com/product.php?product_id=... this one and the other one is also an overkill but you will have enough to run anything. just remember what you house hold wires and fuse/ breaker is 15 amp at 120 volts means max load is 1500watts on the circuit. ohms law.