I will the divide this thread into a couple of parts, for now, it's PROGRAMS [With sub-sections for different OSes, like Windows/Linux) and helpful TUTORIALS (From other sites with said program), which we can use to streamline and centralize all the information here in one thread.
NOTE: This is a WIP! I will edit this OP when I get time (to make it neater and much more friendly), and I ask that you contribute/share your knowledge on any nifty programs out there.
-PROGRAMs
GIMP- Windows/Ubuntu/Mac:
-GIMP is a versatile graphics manipulation package. Consider it as a lighter, free version of Adobe Photoshop.
PAINT.NET- Windows
PAINT- Windows
PAINT is the basic image program that is supplied with all versions of Windows, self-explanatory, you can't do much with this at ALL!
GNU PAINT-Ubuntu
Similar, Ubuntu version of PAINT for Windows, though it has a bit more features than PAINT.
Photoshop CS3-CS5- Windows, iMac
The program that most professional graphics artist uses (very expensive if one were to buy it, and quite a memory hog too if you have a slow computer)
Easy GIF Animator
-As the name states it, this is the easiest program to use when making all of your gifs transparent and setting the timers properly, very user-friendly, and can do much more.
Corel Painter
Blender (3d modeling software)
-Probably the most known 3d modeling software on the internet, it's a powerful tool for creating 3d models.
Pixie
Pixia
TuxPaint
ColorPic
"Ultimate" Paint
i.Mage
PhotoFiltre
"Picnik" (Online photomanipulation site, VERY handy if you don't want to be bothered to download image manipulation programs like Gimp or Photoshop)
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TUTORIALs
-How to make a "space" wallpaper
-Basics to C4D
-GEtting a "blood" effect
-Animations
-"TUTORALIZED" (great tut site)
-Elements/Principles of Art
Spoiler : Tutorial Sites for specific programs :