A Shetland sheepdog.
Source: Photo by en:User:sannse at the City of Birmingham Championship Dog Show, 30th August 2003. Originally from en.wikipedia; description page is/was Sheepdog 600.jpg here. http://en.wiktionary.org/wiki/File:Shetland_Sheepdog_600.jpg
Author: Original uploader was Sannse at en.wikipedia