Paper dimensions

http://www.printernational.org/american-paper-sizes.php

Color Modes

http://www.printernational.org/rgb-versus-cmyk.php

Where to find new brushes

http://browse.deviantart.com/resources/applications/psbrushes/

http://www.brusheezy.com/

http://www.photoshoproadmap.com/Photoshop-blog/2007/10/25/100-awesome-high-resolution-photoshop-brushes/

http://brushes.deviantart.com/journal/3939334/

How to install brushes

For windows
Place the *.abr files into:
Program Files\Adobe\Adobe Photoshop X\Presets\Brushes where X is the version number for your version of Photoshop.

For Mac
Hold the Command (Apple) key and click on the Photoshop icon (or Illustrator, etc.) from the dock. You will be instantly taken to the applications folder in Finder with your app selected. 

Once you are there, all you have to do is select the “Presets” folder, drag your download to the correct location, and your done.

Good tutorial sites
http://www.smashingmagazine.com/2008/01/10/adobe-photoshop-tutorials-best-of/

http://www.dennisplucinik.com/blog/2007/08/28/60-advanced-adobe-photoshop-tutorials/

http://psdtuts.com/

http://www.tutdesk.com/

http://www.photoshoptalent.com/blog/2008/03/08/40-body-enhancement-photoshop-tutorials/

http://dr-photoshop.com/

http://www.printernational.org/

Where to find stock images

http://www.dreamstime.com/

http://www.sxc.hu/

http://www.istockphoto.com/index.php