Adobe Photoshop as well as other Adobe software are arguably the gold standard of graphics and image manipulation.

creativeLive is a great webinar service which is dedicated to professionals teaching all aspects of graphics as well as business (establishing a studio, etc.), and more.

This is a great opportunity to get some free teaching. There are reruns if you miss the original webcast. Courses are also available for purchase.

The schedule can be found here: http://www.creativelive.com/photoshopweek as well as a full listing of the courses and instructors.

I really recommend it to all interested in honing their graphics skills!