A thread to find assets you need, and donate assets that you have. If you've made something cool the rest of us can use, great! If you know where to get some good free stuff, even better! If you know where DB Cooper hid the rest of the money, doubleplus extrabetter!

If you want to specifically use assets from a previous gamejam you can leave a message here, DM the person, or more likely ask for them in the #game-dev channel of the Slack!   Because of how big the list is, any "tools" or "engines" will be found over on the main announce page for the Jam in time. This is just for stuff that is already made and you can use. If you have any other suggestions, please feel free to reply in this thread.
Just a reminder that the Jam will be hosted over at the Itchio. 

Audio:  Sound Image - Thumb Eric Matyas has an amazing and vast collection of game music, categorized and many of it ready to loop. You just need to credit him in the work. Check it out! Youtube Audio Library - Music for YouTube videos and "other content you create." FreeSFX - Sort of random collection of effects, check the license for information on how to accredit them. Free Music Archive - The great and classic home of Creative Commons music, but a wild west of licensing issues. Make sure to carefully check the license for whatever you want, but note that you can search by license! (The amazing Dinosaursssssss, originator of this list, has compiled his faves into a list.  freesound - Creative Commons licensed music and effects. Searchable by license.  FilmSound - Links to more effects. Incompetech - Music, requires crediting under CC. musopen - Public domain classical music. IndieGameMusic - Nice. Media College - Free sfx library.  The Firearm Sound Library - You need loud bangs, they got 'em. NASA Space Sounds - NASA has put all their space sounds on Soundcloud! Wizardjam SoundBank - Zombie Thumb Patrick has curated the best of his music into a handy Soundcloud! You can find a more complete listing of his work along with details on the tracks here.  The Sounds of Sgt.Whistlebotom: A collection of game music from another talented Thumb.     Models:   BlendSwap - Blender artists swap their work under the CC license. TurboSquid - 3D models but they mostly cost money. OpenGameArt - Some sweet looking modular game assets   Textures:  CGTextures - Not allowed to be used in SecondLife, good elsewhere. Texturer - These ones you can totally use in SecondLife. Texturelib - Free Textures!  Good Textures - Royalty free seamless textures & photos. Mayang's free Textures - What it says on the label. Free Stock Textures - Stock Textures, that are...free! Lost & Taken - Hey, this one had an interesting name! But it's the same kind of thing! Zen Textures - Why are you still reading these?! It's just more royalty free high quality textures! Texturegreen - Texturegreen, texturegreen, greenest texture I've ever seen.  Texture King - Bill Murray really made me care about the Cubs win. luGher Texture - He really is a remarkable man, I don't know what losing him will be like. Plaintextures - Free hi-res textures and brushes.  Bricks N' Tiles - Seamless Architectural Texture Generator.  Texturemate - Free textures, brushes, patterns, and design articles.     Fonts: FontSpace - A crazy number of fonts, most of which are free/require some form of licensing.  Google Fonts - Huge number of free to use fonts.  League of Moveable Type - Free and open-source fonts.  DaFont - A fun library of fonts.      Other/General:  Unity Store - Lots of good stuff on here for free, models, scripts, all types of stuff.  TigSource Assemblee - A bunch of really bonkers (good bonkers, the best type of bonkers) sprite sheets/textures and assorted music/effects. OpenGamerArt - 2D/3D art, music, sound effects, and a handful of scripts/fonts. Filterable by license.  Creative Market - Icons/Images/Logos, other things (paid) Kenney Donation Pack - A big set of fonts/icons/tiles/sprites ($1+ donation) Getty Image Library - They have everything, and very liberal licenses of use. Open Clipart - Huge royalty free asset source. Here is their use policy.  The British Library - They just dumped about 1 Million images into public domain, here they are organized by album.
The Aberdeen Bestiary - Gorgeous medieval illustrated manuscripts depicting animals as moral fables. Free to use.  ProcJam Art Packs - 1 3D and 2 2D art and asset packs, totally free for you to use! Created for this year's Procedural Art Jam, they also have talks on using procedural generation in your games.