Minecraft wiki entry for Rail, associated text: An example of a track with curves and ramps.
An example of how to use the tracks as a roller coaster.
A randomly generated misplaced rail found in a mineshaft.
Three more floating rails in a mineshaft.
Villagers riding minecarts with rails below them.
A railroad stop without any redstone switching mechanisms, based purely on the one-way curve intersection behavior.
A polar bear intentionally walking on powered rails due to the fact that it spawned inside a ski resort's ski lifts. This is an example of odd behavior of mobs, since they don't walk on rails.