Zipzoomfly is a very reliable website, though they're mostly known as a smaller competitor to sites like newegg.com or tigetdirect.com
I've placed half a dozen orders for PC parts, though If I had to lodge a gripe against them, they, like amazon.com, can be notorious for raising prices as more orders are being placed for an item.
For example, someone posts a great deal for RAM at ZZF on slickdeals or fatwallet, they must have some algorithm that raises the price of the item a few dollars when an item receives an influx of orders.