We have quite a few art tools on itch.io. Here are some:
- https://dacap.itch.io/aseprite
- https://led.itch.io/tilemancer
- https://kenney.itch.io/assetforge-deluxe
- https://emad.itch.io/jpixel
I wrote a post about game development tools here: https://itch.io/blog/6037/get-ready-for-ludum-dare-game-development-tools
Also you can try browsing our tools page