Allopatric speciation is another way of saying speciation by geographic isolation. Something such as river or other physical barrier causes separation between two groups, causing isolation. This eventually causes lineage to speciate, after the two groups can no longer mate with one another.
Video & Picture
The video posted about the salamders is a great example of allopatric speciation. These salamaders have been separated through allopatric speciation and now live across the state of California.
Here is another video about Speciation looking at different types of birds.