http://www.seamlessexpression.com - Steven Berry's site is a valuable collection of reviews of watercolor workshops he attended. Two reviews I especially appreciate are workshops by Joseph Zbukvic and Alvaro Castagnet.
www.virtualgouacheland.blogspot.com - Erik Tiemens freely mixes watercolor and gouache to make exquisite small landscapes and figures. He includes references to historical periods and artists from the 17th, 18th, and 19th centuries that influence specific works. I attended one of his workshops in 2012 in San Francisco.
www.josephzbukvic.com - Examples of watercolors that embody the best of the long tradition but in contemporary subject matter.
www.wikiart.org/en/john-singer-sargent - A master of both oil and watercolor in the 19th and early 20th centuries. Like Erik Tiemens and Joseph Zbukvic, Sargent used gouache generously in his watercolors whenever the opportunity called for it--the end justifies the means.
www.handprint.com/HP/WCL/water.html - A valuable source of watercolor history, papers, brushes, and techniques, especially the history of watercolor through a brief discussion of artists.