I like mwave.com
I purchased a few things from them and found the packaging very secure and their processing time top notch plus some of their prices are amazing, although some can be higher then competitors so do your research
Shipping was also really fast for the cheapest one
I'd say newegg.com is by far the best and most reliable, they are one of the biggest and most popular sites and if security is a very high condition for you, go there
otherwise, you can usually find cheaper prices on other sites although occasionally newegg will have some amazing prices
also try tigerdirect.com