NewEgg is by far the biggest and most popular online PC hardware retailer. I'd buy from them before anyone else. Sometimes you'll find better deals at other retailers. Among them, mwave would be my next choice. They're just as reliable as NewEgg, occasionally have better prices, but they don't have as much selection. SuperBiiz and Directron are also highly regarded. Zip Zoom Fly used to be very good, but they're reputation isn't what it used to be. Avoid Tiger Direct like the plague.