I was really impressed with Chamartin station in Madrid. It was built in 1982 and connected the high-speed rail, commuter, and two subway lines. But it also had a couple of unused platforms for future expansion. That's the sort of thing we used to do in Toronto.
Here are a couple of pics of the unused platforms, as well as the amazing public art installation. You can read more in my blog post.
The most recent extension of our subway has unused platforms - the island and north platforms at Sheppard-Yonge on the Sheppard line.
Sheung Wan MTR station in Hong Kong was also built with an unused platform for a proposed route that never came. The unused platform has been the subject of a lot of ghost stories and urban legends (such as how the platform was built in a space once occupied by a WWII mass grave, making the platform so haunted that MTR was scared about putting it to use).
