The Holy Monastery of St. Catherine at Mount Sinai now has a very nice looking official website. The website is currently only in modern Greek, though English and Arabic versions are in the works.
The site contains information about the monastery as well as a great collection of photographs of the monastery, surrounding areas, iconography, and some of their manuscripts. It only has one page on Codex Sinaiticus that I could find, that provides a bit of history of the manuscript and a small picture. (Alexander Schick/Stephen Goranson via Textual Criticism list)