You can already try the HTC Vive in Microsoft stores and the Oculus Rift in Best Buy. But where can you try the upcoming PlayStation VR to try before you buy?
You can now demo PlayStation VR is one of 400 Best Buy and Game Stop locations throughout the US. Just in a 50-mile radius from me there are over 20 locations. Assuming you live in or near a big city you shouldn't have a problem.
Sony have a PSVR store locator on their site to help you find a PlaySation VR demo location.