Often the most overlooked item in a computer is the power supply.
I will not go into detail as to why you should pick a good power supply, other than to say cheap power supplies rate their PSUs by "peak" power [or power that spikes to that wattage then drops]. You want a power supply that is rated by "continuous" power.
I like a lot of the Corsair power supplies because some of them are made by SeaSonic, a good company. There are other good companies, however, some of them are very expensive.
Here is a link to Newegg Corsair PSUs:http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007657%2050001459&IsNodeId=1&name=Corsair
Here is a link to Certified 80 Plus [or higher]:http://www.plugloadsolutions.com/80PlusPowerSupplies.aspx
Here is a link to Certified 80 Plus for Corsair [to make it easy, as the above chart is difficult for someone not familiar with technology].http://www.plugloadsolutions.com/80PlusPowerSuppliesDetail.aspx?id=25&type=2