Accessed through a back room of The Leaky Cauldron, it's a wizard shop paradise. Several shops line the streets and crooked and darker Knockturn Alley which houses shops that cater more towards the dark arts.

Shops:

The Daily Prophet Office
the office of the wizarding newspape

Borgin& Burkes
a Dark Arts antique shop located in Knockturn Alley, containing such things as a cursed opal necklace

Eeylops Owl Emporium
sells owls and supplies such as owl treats and cages. Inside, it is dark and full of a low, soft hooting, rustling and the flickering of "jewel-bright eyes

Florean Fortescue's Ice Cream Parlour
under the management of the owner Florean Fortescue (founder and shopkeeper), sold ice cream, including sundaes, which could be enjoyed at outdoor table

Flourish & Blotts
sells a great variety of magic books, including textbooks for Hogwarts courses and other books of general magical interest. In the back there is a corner devoted solely to divination, which includes a small table stacked with titles like Predicting the Unpredictable: Insulate Yourself against Shocks and Broken Balls: When Fortunes Turn Foul. Another small display contains the book Death Omens: What to Do When You Know the Worst is Coming.

Gringotts Wizarding Bank
the only known bank of the wizarding world and it is operated primarily by goblins. A snowy white building, near the intersection of Knockturn Alley and Diagon Alley, Gringotts towers over all neighbouring shops. Customers pass through a set of bronze doors and then silver ones before entering the lobby. The main floor is paved with marble and has long counters stretching along its length. Within, wizards and witches keep their money and other valuables in vaults that are protected by very complex and very strong security measures. The vaults extend for miles under London and are accessible through rough stone passageways and then by means of magic carts that travel speedily along their tracks. Gringotts also offers Muggle-Wizarding currency exchange.

The Leaky Cauldron
a pub and inn for wizards, located on the Muggle street of Charing Cross Road in London, offering food, drinks and rooms to rent. It was founded by Daisy Dodderidge (1467–1555) in 1500 "to serve as a gateway between the non-wizarding world and Diagon Alley." The current barman and innkeeper is a wizard named Tom.
On the main floor, the inn has a bar, several private parlour rooms, and a large dining room. On the upper floors, there are a number of rooms available.The pub serves as a way of entering into Diagon Alley from the Muggle world for Muggle-borns and their parents (both of whom, until the first letter from Hogwarts, have no magical knowledge or means of entering). The rear of The Leaky Cauldron opens onto a chilly little courtyard where a brick (found by counting three up and two across) is tapped three times.

Madam Malkin's Robes for All Occasions
a clothing shop next to Flourish & Blotts. It sells robes and other clothing, including the standard Hogwarts-required plain black work robes, and dress robes. Madam Malkin, a squat witch who wears mauve robes, and her assistants will tailor the robes to fit right in her shop.

Magical Menagerie
a magical creature shop that in addition to selling magical creatures also offers advice on animal care and health. The shop is very cramped, noisy and smelly, due to every inch being covered with cages. Among the creatures in the Magical Menagerie are enormous purple toads, a firecrab, poisonous orange snails, a fat white rabbit that can turn into a silk top hat and back, cats of every colour, ravens, puffskeins, and a cage of sleek black rats that play skipping games with their tails.

Ollivanders
a fine wands shop described as "narrow and shabby, with a sign that reads Ollivanders: Makers of Fine Wands since 382 BC in peeling gold letters over the door. The only display in the window overlooking Diagon Alley is a single wand lying on a faded purple cushion in the dusty window. Within, there are countless narrow boxes piled neatly right up to the ceiling and a spindly-legged chair" (Hagrid, however, breaks it after he sits upon it).
Mr Ollivander, the pale-eyed, white-haired shopkeeper, makes and sells magic wands to witches and wizards as they enter school or break their old wands. He remembers every wand he has ever sold. To determine the best wand for a witch or wizard, Mr Ollivander measures various body parts (including, in Harry's case, between his nostrils) and then checks the reactions of various wands to the buyer, a process to which he refers as "the wand choosing the wizard."

Potage's Cauldron Shop
ells different varieties and sizes of cauldrons, including copper, brass, pewter, silver, self-stirring, collapsible, and solid gold

Quality Quidditch Supplies
sells broomsticks and Quidditch-related items. The store windows often draw young customers to gaze longingly at the merchandise. Its most famous items on display are the Nimbus 2000 and the Firebolt broomsticks,

Slug and Jiggers Apothecary
sells scales, potions and potion ingredients. The shop is quite fascinating despite its very bad smell (a mixture of bad eggs and rotten cabbage). The inside includes barrels of slimy stuff on the floor, jars of herbs, dried roots and bright powders on the shelves, and bundles of feathers, strings of fangs and snarled claws hanging from the ceiling.

Gambol and Japes
is a wizarding joke shop. It is briefly mentioned in Chamber of Secrets, where Fred, George and Lee Jordan stock up on "Dr Filibuster's Fabulous Wet-Start, No-Heat Fireworks."

Stalls
As well as many shops, Diagon Alley also contains small stalls. These stalls sell a wide range of things; including magical sweets

Telescope Shop
Sells different kinds of telescopes for the study of astronomy

Twilfitt and Tatting's
s a wizarding clothing shop located in Diagon Alley

Weasleys' Wizard Wheezes
Weasleys' Wizard Wheezes is a popular joke shop that started as a small school business created by Fred and George Weasley in the fourth book. It opened its doors at Number 93 Diagon Alley in the summer of the sixth book, using Harry Potter's Triwizard Winnings as starting capital. Weasleys' Wizard Wheezes sells joke and trick items, useful novelties, and Defence Against the Dark Arts items.
Fred and George started using the name "Weasleys' Wizard Wheezes" in Goblet of Fire for a mail order business selling merchandise, including sweets to help students skip classes. To run their own joke shop had always been their life's ambition. An ambition they were able to realise when Harry gave them his Triwizard Tournament winnings of a thousand Galleons. After an early departure from Hogwarts in Order of the Phoenix, the two Weasleys set up their shop in Diagon Alley, which quickly became a huge success.

The Poulsbo Cafe
The Poulsbo shop is owned by Hazel Aspen Riversong, it was created by her grandmother many years ago, and Hazel has recently re-opened it as a cafe. Her family used it to get out of America when there was an evil wizard there (read her history). The cafe was named after her grandfather and so she kept it that way. The outside makes the building look like it's all crooked. The inside is like a little country house. It's very soft, and although kind of girly, it's not overly frilly. The walls are light pink stripes with cream stripes up top, and the bottom is wainscoting. The shop has green, yellow, and blue accents. The chairs are high-backed and very plush and comfortable. The tables are miss-matching wooden round tables. Above the tables are floating glass orbs that have color changing fire inside. Lanterns on the walls light the inside along with a massive carved wood fireplace. Up in the crooked vaulted ceilings is basically a rat and cat haven. Both rats and cats live happily together, and they often come down to cuddle with customers that will let them. They aren't however, allowed were the food is made. And mini brooms and dustpans are always going around to get the dust and hair up. Hazel has created a ton of different kinds of sweets, treats, and drinks. She makes teas and coffee, juices, and the like. She serves lunch and dinner also, and with dinner you can order home made ales and wines.

After Hogwarts...