As noted on Stoa, there is a beautiful new website that provides high-quality photos of inscriptions (about 800 of them) relating to the mysteries of Demeter and Kore at Eleusis: Mysteries at Eleusis: Images of Inscriptions (hosted at Cornell University Library)If you are not familiar with the mysteries and would like some background first, you can read short discussions about the mysteries generally on my site here and about the Eleusianian mysteries here, as well as the mysteries of Dionysos, Mithras, and the Great Gods (of Samothrace).