SBB trains live on www.swisstrains.ch
This site is still in ALPHA-phase. The current view is based on the Swiss traintimetable, and does not yet show the actual GPS-positions of the trains. But, as Swiss trains are almost always on time, most of the time the position is accurate.

One of the coolest functions is one that is a bit hidden: click on a moving train, and click in the unfolding menu on the button “Follow”. This will show you from a bird’s eye view via satellite images, the moving train.