Virtual Reality is a simulated artificial environment created by computer programs and consumed by users in such a way that the barrier of disbelief is suspended and the user accepts it as reality. Current state of virtual reality is experienced through two senses (out of five): vision and sound.
State of the art Virtual Reality: Oculus Rift
Current options for consumers are limited to a few companies that sell virtual reality head mounted displays. The best option is the Oculus Rift. This HMD is by far the best on the market in quality, experience and availability of applications, games and experiences. And it is also one of the cheapest.
There are other options on the market but there is hardly any software available for them. Sony has announced an HMD for the PlayStation 4 but it will not be for sale until somewhere in 2015.
On the other hand, the Oculus Rift is available right now as a developer kit. The first version of the developer kit has been sold 60,000 times. And now the second version of the developer kit is in pre-order. The DK2 pre-order will however take a while to be shipped. Estimated shipping starting in july 2014. That is a long wait!
The DK1 sale has been stopped. So, you cannot buy a DK1 or DK2 and get it delivered right now. Luckily you can still buy one from places like Amazon.