When I'm buying parts/supplies for myself or clients my order of companies is simple:
1. NewEgg
2. Amazon
With Amazon Prime and $3.99 overnight shipping, and their absolutely no hassle return policy, I can't recommend them enough. I bought a 70lbs color laser printer for a client in dire need last week and it arrived the very next day, shipping thanks to Amazon Prime, $3.99 versus the $129+ it would have cost me from any other supplier.
With that said, be careful when buying on Amazon that you are actually buying from Amazon.com and not one of their associated vendors. When buying from an associate you deal with different shipping, and most importantly, different customer service and return policies.