A collection of graphics with Public Domain,CC-BY-SA,GPL,BSD,MIT licenses - anything allowed to be used in your free or commercial game, as long as you credit the original producers.
In case you also need free to use game music, there is a separate repository to check out: https://github.com/saniv/free-game-music
Unfortunately OpenGameArt.org curators believe that plundering open source repositories for art is unethical and damaging to site's reputation, even if license allows that. (Full story: http://opengameart.org/forumtopic/censored-broforce-sprites-and-game-ready)
Clint Bellanger has stated that well:
We could instead only allow artists to upload their own art. Most other sites operate this way. It would remove any question about whether an artist is choosing the correct license or intending their art to be used in competing games. Then adding new art to OpenGameArt would be contacting an artist and inviting them to also share their art with us.
In other words OpenGameArt.org is more like gallery and community for arists, instead of being an archive of free game art, that programmers can easily use.
Contrary to OpenGameArt.org's curators, FreeGameArt collection doesn't care about ethics or morals, only about law. So FreeGameArt will try to collect here free art inappropriate for OGA and the art, which original authors decided to pull out of free use or changed its distribution license to the less free one (the case with Monster Rpg 2).
Broforce sprites, in particular, are pesent too: https://github.com/saniv/free-game-art/tree/master/sideview/broforce-sprites
As well as a few unique spirtes, like the isometric Wikipe-tan https://github.com/saniv/free-game-art/blob/master/isometric-unsorted/wikipe-tan.png
And a few sprites drawn completely from scrach by myself: https://github.com/saniv/free-game-art/blob/master/isometric-unsorted/sprites-by-nikita-sadkov.png
If you have free art which is inappropriate for OGA (i.e. CPL or BSD licensed artworks, like SpriteLib by Ari Feldman), you can send a pull request or FreeGameArt can link to your repository.
Enjoy!