Speaking as a graphic designer, I'm with Steven on this one. Most of the links above are good for teaching the practical skills of how to create artwork, which is definitely an important skill that graphic designers need. However, to actually design requires understanding of the elements you're working with (line and shape, colour and tone, space, scale, type and pictures etc.) and how to use them to fit the purpose for which you're designing (what's your brief? who is the end user? what does the design need to achieve?). Think of it this way, if you wanted to be a doctor, it's not enough to know that this illness requires that antibiotic; it's important you understand how the body works, how drugs work and how to diagnose an illness in order to choose the right therapy.
So with that in mind, I would agree with the recommendations of [Before and After Magazine and add [URL="http://www.creativepro.com/"]Creative pro](http://www.bamagazine.com/) as great resources on the theory of design as this is what will ensure your graphics work. They both have enewsletters that you can sign up to; BA magazine also offers a forum if you purchase a paid subscribe to their magazine which seems to be a really good community of designers that could give you support while you learn the ropes.
If you want to work as a graphic designer, another good blog to follow is Graphic Design Blender which gives great advice on how to run a profitable freelance design business. They talk a lot about finding your niche, which is where the artworking links above come into their own. What kinds of projects do you want to design for? There's so much out there that could be learnt, make sure you focus on one area at a time so you can really get good at it!