Power supply. Without a reliable quality power supply, the rest of your computer is useless. It's not uncommon for cheap power supplies to destroy other parts of a computer when they malfunction. The Antec NEO isn't bottom of the barrel but I would still call it low end. You don't need a $300 1200-Watt PSU, just a Corsair TX650V2, I think they're around $80-$90. Try and get it on a mail in rebate, I've had 100% success with Corsair's mail in rebates. They come back fast and are in the form of a Visa card that you can use anywhere, even Paypal.
Trust me, when you open the box for that PSU and feel the weight and solid build quality, you will know it was money well spent. You can rest easy knowing that if you have ANY problem with it in the next 5 years (long time for a computer) that you can return it under warranty from a company that's well-known for great customer service and fast RMA processes.
*EDIT*
Right now it's got a $20 mail in rebate. $65 when it's all done. Damn good deal, wish I had a customer lined up that wanted a build now.
Check out this review on JonnyGURU (pretty much THE go-to guy for solid and extensive reviews) for the TX750V2:
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=230