Getting Started: Where to Buy

So, full disclosure, this list is mostly of personal opinion, and there are many good stores that will likely get left out, but for someone just starting out in the game and trying to figure out where to even begin looking, this is good enough.

One of the main traps I want to warn against when shopping for airsoft goods is that there are just as many online retailers in China as there are in the United States. That said, there is nothing wrong with a lot of the Chinese retailers you'll find. In fact, many overseas retailers carry items that are incredibly hard to find in the US. However, typically speaking you can expect longer ship times, higher shipping costs, more finicky package tracking, and more hassle if something goes wrong.

Also, store geography is important to some people (including me). I'll also list where each store is located so you can get a sense of how long items should take to arrive.
Let's get started:

AirsoftGI and GI Tactical

AirsoftGI is one of the biggest retailers in the country. AirsoftGI is headquartered in California, however GI Tactical is located right here in VA (Richmond, specifically). Both stores have a good selection of quality gear, and their online store is a great place to browse for guns and equipment.

EVIKE

Evike is also one of the biggest retailers in the country. They too are located in California. Good selection, good place to browse.

Amped Airsoft

While Amped doesn't boast the largest collection of equipment, they make up for it in selling quality products. Their staff is also super friendly, and they are located relatively nearby in PA.

Roanoke Airsoft

These guys are just up the road an hour from Blacksburg in Roanoke, VA! Small storefront, but outstanding supplies for someone just starting out. Bonus points for being able to hold things before you buy them.

Other noteworthy companies:

Airsoft Atlanta in Atlanta, GA
HotSpot Airsoft in New York
AirsoftSmith in Ohio
Tiger Tactical in New York
Fox Airsoft in Colorado

Popular Chinese Retailers:

Redwolf Airsoft
eHobby
WGC Shop

Reminder: this is not an exhaustive list. In your searching you will find many many more. These are just good places for starting out.