This site is the best starting place online for learning Church Slavonic.
This is a program that teaches Church Slavonic prayers and pronunciation. It has RealAudio and MP3 versions of common prayers and hymns, as well as other interesting resources. It is an excellent site for developing an ear for the sound of Church Slavonic and its stresses and phrasings.
A collection of many Church Slavonic-related resources, including fonts, scholarly material, and more.
Online Liturgical Texts in Slavonic
This is a collection of links to prayers, services, and music in Church Slavonic.