I came across the Gimp User Group website and it's got some great content. They have really useful Tutorials for GIMP users and I found them pretty impressive. They cover some of the most basic techniques for creating some some of the most common and stunning effects used in 2D rendering. The tutorials covered both basics and advanced topics. Of course, most instructions are applicable to Photoshop users as well, using the corresponding functions. More discussions about user submitted artwork and tips in general can be found at the
Other interesting features include the Gallery with artwork submitted by members and a decent collection of Textures and Scripts.
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Usefull information and all is good arranged. glucometer