Here's an interesting vid by Tom Hess.
This video could have been given a better title -- it's a bit more than just a 'guitar solo lesson'. But any reference to 'music theory' or 'non-chord tones' would have caused the shred horde to gallop a mile away. (Just kidding!)
Starting out by playing over a Dm tonality, Hess demonstrates the use of non-chord tones to connect between notes. Bending from a non-chord tone up to a chord tone, Hess releases the bend gradually so it lands momentarily back on the non-chord tone before resolving it a whole-step lower. Nice stuff.
Hess's observation of the 9th of the scale is really spot on, "It's a very lonely kind of note.. it sounds very isolated, very longing.."
Hess has one of those really wide modern rock vibratos. Hitting a bent note without vibrato and then hitting it again with a wide fast vibrato, he demonstrates a more dramatic way of applying the technique that "just grips your throat". I remember Yngwie also talking about this in an interview from a long time ago.
Hess's take on music theory is refreshing: "How do I recreate this and how do I recreate this all the time -- and start memorizing what different feelings sound like and be able to identify them. There's nothing that you can play that music theory can't explain. When you know what those things are, you can recreate any emotion that you want, anytime you want."
Pretty cool, and a must watch. Check out Hess's website at http://tomhess.net/ for more.