Image SitesPSDCovers.com - A site full of Photoshop actions to turn 2D designs into 3D designs in minuntes, i.e. a flat book cover into what looks like a 3D book etc. Includes some tutorials on how to use the actions.
A tutorial by psdbox.com on how to use one of the above actions to best advantage.
Free stock images from sxc.com - images free to use
morgueFile.com - This morgue file contains free high resolution digital stock photographs and reference images for either corporate or public use. The purpose of this site is to provide free image reference material for illustrators, comic book artist, designers, teachers and all creative pursuits.
Freerange Stock Community
StockVault.com - free to use images for non-commercial purposes.
FreePick.com - site to help find free images
The Russell Brown Show - lots of useful imaging info including Adobe scripts and actions.
Lost and Taken - free textures
CGTextures.com - more free textures, but please read the FAQ to make sure you know what you are allowed to use them for and what you aren't
OSF Costume Rentals - This is actually a costume rental site, but I think it is a great resource for referencing costumes in illustrations.
Figure and Gesture Drawing, PIXELovely.com - Tools for Self-Educating Artists
Getty Images - now has an embed option for Bloggers on some of their stock footage.
Free Art books listed out from Archive.org
Colour Pallete Generator - generate a colour pallete based on an uploaded image.
Brush sitesbrusheezy.com - many of the brushes are free with accreditation, but check the licences.
Royalty Free Pay for Image SitesCutcaster
Font Sites (always check the license on the font before using it)1001freefonts
Font Squirrel - all licensed for commercial use