Orthotracts Music Page - 100s of MP3 files of Orthodox Church Singing

Reader John's E-Kliros – Music In Progress for St. Nicholas Church, Saratoga, CA (includes some resources for learning modern Russian Stichera, Troparia and Podobny melodies)

St. John Chrysostom Russian Orthodox Church - Liturgical Sheet Music in English

Православный клирос - massive collection, mostly PDFs and choral compositions and chant arrangements

Seminaria.ru

ROCOR Monasteries - West Virginia and California