Doug Cox has been teaching dobro lessons and producing videos since before the DVD was born. He's not just a partner in the Learn Roots Music company, he's also the companie's most prolific teacher with four DVDs on offer (including his "Understanding Slide Guitar" title).
Just as with the banjo, the dobro and lap-style guitar are staples in bluegrass world, but can jump genres into some unexpected territory. For example, Ivan Rosenberg's Bluegrass Dobro is for the modern bluegrass player looking to integrate more advanced harmony into their repertoire.
Steve Dawson presents a unique approach to C tuning on the Weissenborn guitar that will open your eyes and ears to extended harmony on the instrument, not to mention his authentic lesson on Hawaiian guitar.