Equipment & Gear Recommendations:

There are tons of trekking equipment stores in Kathmandu, a bunch in Lukla, and over 20 gear stores in Namche Bazaar. It's best to bring as much essential gear from home as you may not be satisfied with the quality you find in Nepal. There are official brand name stores (Mountain Hardware, Marmot, etc) however the prices are comparable with those in the Europe & North America.  Many of the stores in Kathmandu, Lukla, & Namche Bazaar sell used and "new" knock off items that while adequate, are not as high quality as the real thing.  While you want to keep your pack weight light (if carrying your own pack) you can also hire a porter to carry your equipment. 

Here are some essential gear recommendations for the trek:

-Trekking Backpack. I recommended Osprey, Gregory, & Arcteryx however it's most important you find a pack that fits you well, has enough storage, and a relatively comfortable hip belt.  We carried our backpacks the entire way and I my pack (male) weighed about 18-20 lbs however you can make it much lighter.
-Sleeping Bag: You need a warm sleeping bag past Namche Bazaar as most lodges do not have adequate insulation and the blankets they provide might not provide enough warmth & some can be old & worn. I made a mistake of renting a sleeping bag in Namchee Bazaar. Although it kept me warm & the quality was good it gave me contact dermatitis which required antibiotics when I returned to Kathmandu.  Believe me, it's worth the weight. 
-Light/Medium Weight Rainjacket/shell: It's likely that you will encounter some rain in the lower elevations and possibly snow in the higher elevations. It's imperative you stay as warm and dry as possible. I recommend Arcteryx and Mountain Hardware brand jackets. 
-Trekking socks and Lycra/Nylon underwear. I prefer Darntough medium weight socks and Smart Wool heavy-duty trekking socks. For underwear, I like Exofficio which lasted for days without smelling or needing a wash.  For women, a lightweight wool underwear (Ibex) are breathable and keep you warm in wet conditions.
-Trekking pants and fleece: Lightweight pants & shorts that are well made and you can wear for several days on a tough trek are essential for the EBC trail. I find that Kuhl pants are lightweight and durable for the trek in the warmer months. Long underwear or a lightweight fleece will keep you warm in the cold nights and mornings. Trekking in winter requires warmer clothing. Remember to layer and bring enough gear to stay warm during cold nights. 
-Trekking Poles: Trekking poles are imperative for taking weight off of your legs, knees, & back especially on the descents, and saves your feet on steep sections. 
-Smartwool long/short sleeved shirts: Like polypro although warmer and can last days and even weeks without smelling. These are great layers that are light weight, breathable, and can take a beating on the trail. I prefer the brands Smartwool (tee shirts), Merino Wool, & Icebreaker. You can also purchase these brands in long underwear.  Remember, cotton is not breathable and smells.
-Lightweight Sun Hat: The sun can be really strong in the upper Khumbu and a lightweight hat that covers your forehead and back of your neck can be essential to avoiding sun burn. I wore mine everyday past Namche Bazaar.
Bandana/Face Cover: To help keep the sweat off your face and to cover your nose & mouth while walking on the dusty sections of the trail. 
-Headlamp: In case you get lost in the dark or need light as many lodges have spotty electricity. I prefer Petzel or Black Diamond.
-First Aid Kit: All the essentials of a light weight first aid kit are helpful, and although you can purchase many items in Kathmandu (including antibiotics) and in Namche Bazaar you will need various bandages, antibacterial cream, sun block, and various medicines. You can also include diamox if you need it (I did not like it) and Cipro for your stomach. 
-Sunglasses: Do not forget quality sunglasses or mountaineering glasses  with UV protection as the sun is very strong above 3000 meters and reflecting off the snow can cause snow blindness without proper eye wear. I used Native Eyewear sunglasses that worked great.