Spintronics is "Spin based electronics". The idea is to use the electron's spin, as well as it's charge. Electrons can spin in two directions (Spin-Up, Spin-Down, which is actually clockwise and anti-clockwise), and the spin is detectable as weak magnetic energy. Hopefully Spintronics will allow us to do more "work" than electronics, with less effort.
There are many possible usages of Spintronics. One of the obvious ones is memory. MRAM is based on Spintronics, and it promises to be a fast, small and non-volatile memory.
In the future we might see Spintronics based transistors, which will allow us to replace electronics circuit boards with Spintronics ones.
So why is Spintronics better than Electronics?
For starters, Spintronic device do not need an electric current to retain their "spin". That means, for example, that MRAM is a non-volatile memory, like FLASH. Spin is more "relaiable", and such devices will operate better in high temperature or raditation environments. Theoretically Spintronic devices will be smaller, faster and more powerful than electronic ones.
Are there any Spintronics-powered products today?
Spin-Valves, which are used in Hard-Disks and sensors today, use Spintronics. Also MRAM, which is based on Spintronics, is advancing nicely, and EverSpin (formerly part of Freescale) have started selling 4-Mbit MRAM modules. There are several Spintronics-based sensors which are also available today.
As Spintronics uses the spin of electrons, the new field of Valleytronics uses the valley degree of freedom in certain semiconductors - such as graphene or other materials.