Online Lessons

I came across another good music site the other day. This one is devoted to learning, is easy to use, and thorough. Here you can find simple lessons on the staff, clefs and ledger lines, note and rest durations, measures and time signatures, key signatures, major and minor scales, intervals, etc. It also goes beyond the basics and to more advanced theory:
Music Theory

This is a very handy little tool for learning the notes on the guitar neck. Test your knowledge:
Fretboard Trainer

The same site has an ear trainer. Knowing your intervals is a must for any type of musician:
Ear Trainer