Bass 
8 Notes(7)
8notes.com focuses on traditional and classical lessons. They have over 100 free violin pieces in their own collection and hundreds of melodies for traditional violin, pipe and other treble instruments. Each song has a downloadable gif or pdf file and you can also listen to the midi version of the song. You have to [...]
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Institute of bass
Instituteofbass.com is a useful site with 22 lessons. The site is aimed specifically at the art of contemporary bass playing and the study of bass tradition. The articles under each lesson are extensive and informative. But, a few of the lessons don’t have tablature which could cause a problem for those who don’t read music, [...]
Funky Chops
Funkychops.com offers bass lessons with a focus on slap bass and learning by ear.
The site offers some free audio and video samples of the lessons which look pretty good.
Active Bass
Activebass.com is a very informative site and includes a lot of lessons & resources. The site boasts over 8,000 bass lessons in total. The bass lessons are separated into 22 different genres.