Browsing around various garden and design related sites, Gardenvisit.com put together by garden scholar Tom Turner has excellent information relevant for gardeners and landscape architects alike.
The site map gives a good overview of the breadth of information available, from bios on famous garden designers, essays on gardens and parks, to a section on garden history, among may sections.
The site is a good resource for those looking for photographs, travel information on gardens, design principles, and garden history.