Below are two of my favorite places to purchase photography gear and equipment. Amazon is of course great, especially if you have Prime. When it comes down to it, though, I still prefer to purchase from dedicated photography dealers.
B&H Photo Video may be the single largest photography dealer in the United States. Located in New York, they have a massive selection and ship everywhere. Prices at B&H are relatively fair and competitive with Amazon, especially during sales.
Midwest Photo Exchange (MPEX) is similar to B&H, but on a smaller scale, and out of Ohio. Their shop provides classes for local patrons, and their blog is enjoyable, as well. They have most of the hot items in stock, as well as many more affordable (but still awesome) packages from up-and-coming brands. They also have a partnership with Strobist® for some great beginner OCF kits.