The easiest thing for me to do is to send you to The Parasitic Plant 
Connection, a site where you will find lots of images and information, including links to most other parasitic plant sites.
Other sites containing (taxonomic) Cuscuta information:
Atlas of Alabama, Florida & New York Vascular Plants: distribution maps & synonyms for taxa ocurring in Florida.
Calflora: distribution, synonymy, ecology & biology for the Californian species.
Checklist of the Vascular Plants of Washington State. University of Washington Herbarium.
Convolvulaceae Unlimited: a growing website with genus descriptions, geographical distribution, and, in the future, species info and images.
Flora of Texas Database: herbarium specimens, images, references.
Digital Atlas of the Virginia Flora: geographical distribution maps & comments.
E-Flora BC: Electronic Atlas of the Plants of British Columbia: complete information about the 5 species of Cuscuta growing in British Columbia: distribution maps, descriptions, line drawings, ecology, status information in BC, and more!
Flora of China: identification key and descriptions for Chinese species.
Flora of Missouri: A checklist of the species from Missouri following the treatment of Dr. George Yatskievych 2006. Steyermark’s Flora of Missouri. Vol. 2, Missouri Botanical Garden Press [Better use the book].
Flora of Taiwan. Vol 4.: identification key & descriptions for the 3 species that occur in Taiwan (plus line-drawings of Cuscuta australis).
International Plant Index Name (IPNI): names information.
Iowa Plants: Cuscuta (Richard Lutz)
Jepson Flora Project: absolutely everything you need to know about the Californian species is here!
Michigan Flora: identification key, ecology, images
New England Plants; Go Botany: images, description, habitat, distribution
Oregon Plant Atlas: checklist, distribution maps.
Smithsonian National Museum of Natural History. Botanical Type Specimen Register: photographs of the type specimens (please note that we could not link our galleries to the type specimens from US).
Taiwan – research information on Cuscuta in Taiwan.
USDA Plants: profiles for the U.S.A. species
USDA, Germplasm Resources Information Network
W3-TROPICOS: names data & references; chromosome numbers, photographs of the types (please note that we could not link our galleries to the specimens we used from Missouri Botanical Garden Herbarium).
Western Australian Flora: distribution, descriptions and photos of Australian species.
Wisconsin Botanical Information System: checklist of species, synonymy, didtribution maps, floristic ratings.