(Semi-random order, not all tiles are used even if added to the set).
Lanea Zimmerman (Sharm)
http://opengameart.org/content/tiny-16-basic
http://opengameart.org/content/16x16-overworld-tiles
http://opengameart.org/content/rpg-indoor-tileset-expansion-1
CC-BY 3.0 / OGA-BY 3.0
Scott Matott
http://opengameart.org/content/instant-dungeon-v14-art-pack
http://www.indiedb.com/games/instant-dungeon
OGA-BY 3.0
Russpuppy
http://opengameart.org/content/rpg-tileset
http://russpuppy.com
CC0
Stephen Challener (Redshrike)
http://opengameart.org/content/16x16-16x24-32x32-rpg-enemies-updated
http://opengameart.org/content/rat-and-rat-king-overworld-antifarea-style
http://opengameart.org/content/a-load-of-overworld-34-rpg-sprites
CC-BY 3.0 / OGA-BY 3.0
MrBeast (Commissioned by OpenGameArt.org)
http://opengameart.org/content/cave-tileset-0
http://opengameart.org/content/desert-tileset-0
http://opengameart.org/content/sewer-tileset
http://opengameart.org/content/objects-for-16x16-tilesets
CC-BY 3.0
Ogrebane
http://opengameart.org/content/16x16-tiles
CC0
CharlesGabriel
http://opengameart.org/content/halloween-gift-for-oga
CC-BY 3.0
surt
http://opengameart.org/content/forest-tiles
CC0
Hyptosis
http://opengameart.org/content/lots-of-free-2d-tiles-and-sprites-by-hyptosis
CC-BY 3.0
Kenney http://opengameart.org/content/50-rpg-sound-effects http://opengameart.org/content/51-ui-sound-effects-buttons-switches-and-clicks http://opengameart.org/content/63-digital-sound-effects-lasers-phasers-space-etc
hit.ogg:
8-Bit Sound Effects Library by Little Robot Sound Factory
www.littlerobotsoundfactory.com
http://opengameart.org/content/8-bit-sound-effects-library
CC-BY 3.0