You can choose between a couple of laptops, netbooks, desktops, and you can even buy various accessories. Most major brands are there: Acer, Dell, HP, Sony, Asus, Lenovo, and a couple of others; you can also filter the products by price, screen size, processor, memory size, and weight.
As far as accessories go, they're mostly of Microsoft origin, as the company produces a wide variety of mice, keyboard and other computer paraphernalia, but you can also buy other companies' products, like this Kingston USB flash drive. Products from Microsoft's arch-enemy when it comes to computer accessories, Logitech, are nowhere to be found.
After the announcement about opening two brick-and-mortar stores, Microsoft has taken another step in the direction of selling third party hardware. We'll see how far they're willing to take it.