The first link on this list provides an explanation of Lexile to grade level conversion. The other links provide methods for determining interest, grade, Guided Reading, and Lexile levels.
Edutopia: Billed as "what works in education," this site offers videos, strategies, and classroom guides for a variety of educational purposes.
Discovery Education: Although this is a subscription site, it offers a number of free resources for teachers.
Edublogs: Allows you to create and manage student and teacher blogs easily and securely.