You may have heard of David Wallimann - I just found his stuff this morning.

I really enjoyed his presentation of this material. Not just "guitar stuff", but very insightful and well prosented discussion on the topics.

Modal Chord Progressions
https://www.youtube.com/watch?v=CTYJgmEvcKA&feature=player_embedded

Secrets to great improvisations
https://www.youtube.com/watch?v=yNh4kaHiSHM&feature=player_embedded