"A magical collection of interactive music theory tools and visual references to learn music online for free."
This is such a fun site that has so many different free modules. Bookmark it if you need an online tuner. Need Ukulele chords? How about some free sample packs (and even synth presets)? An online Xylophone? Or even a free Kick generator that you can save out .wav files in different resolutions to use in your own music or sampler.