Links
Krita
Creators of Krita. An amazingly good and free digital painting program. Give it a try.
MediBang Paint
A fantastic and free digital art and illustration program geared towards making manga/comic-books, but great for making game art too!
GameArt2D.com
GameArt2D.com is a place to buy royalty free 2D game art assets. With more than 100 game assets listed. From character sprites, tilesets, to complete GUI
craftpix.net
Free and Premium Game assets. This includes many animated game characters complete with full Spriter projects.
GameDeveloperStudio.com
GameDeveloperStudio.com offers the largest collection of single styled 2d game assets on the internet. At over 10,000 2d game assets.