Dr. Gunter Gerlach of the Munich Botanical Gardens has numerous photos, and information about the Catasetinae, Stanhopeinae, and Coryanthes. Genera include Acineta, Catasetum, Clowesia, Coryanthes, Cycnoches, Gongora, Houlletia, Kegeliella, Lacaena, Mormodes, Paphinia, Polycycnis, Schlimmia, Sievekingia, Soterosanthus, Stanhopea, Trevoria, and Vasqueziella.
Orchids of the Pleurothallid Alliance by Lynn O’Shaughnessy has a lot of information and photos of many Pleurothallid species.
Bulbophyllum from A to Z by Rudolf Hromniak and Anton Sieder has a photos of Bulbophyllum and some other species.
The Genus Dendrochilum was established by Trey Sanders to help identify Dendrochilum species, and has photos, and descriptions of all of them.
Cultivadores de Encyclias is a Flickr site that has many photos of the species, and some descriptions.
Florent Borderie Nature Photography has some excellent photos of orchids in the wild on Réunion island, and in France.
The Slipper Orchid Alliance is dedicated to the preservation of, and education about, all lady-slipper orchids, and has some excellent photos, and other information.
Orchids of New Guinea has concise information on all 142 genera, and includes a richly illustrated checklist of all taxa currently known to occur in New Guinea, almost 3,000 at current count.