Premium
http://oryxdesignlab.com/product-sprites/oryx-sprite-mega-pack
https://www.gamedevmarket.net/member/7soul/
https://www.gamedevmarket.net/member/thkaspar/
https://gamedevfort.com/store/category/2d-assets/?page=1
http://kenney.nl/assets?s=rpg
Free
Please review license instructions before using any of these.
http://opengameart.org/content/dungeon-crawl-32x32-tiles
http://opengameart.org/content/roguelite
http://opengameart.org/content/blowhard-2-blow-harder
http://opengameart.org/content/a-blocky-dungeon
http://opengameart.org/content/cowboy-game-sprites
http://opengameart.org/content/rpg-town-pixel-art-assets
https://github.com/Yxven/roguelike/tree/master/assets/DawnLike_3
http://www.lostgarden.com/2006/07/more-free-game-graphics.html
http://www.rpg-palace.com/visual-resources/tilesets-rmxp
http://www3.wind.ne.jp/DENZI/diary/