I really suck at graphics / music / 3D modeling / animation and it's a must-have when you have a hundred hobby game development projects you're working on. I'm looking for different quality sources on the web that provide free resources.
[EDIT] Some resources given by the answers, in bold the biggest resource per section:
MODELS
SPRITES
ANIMATED SPRITES
CLIPART / VECTOR BASED
PHOTOS
TEXTURES
MUSIC
SOUND EFFECTS
OTHER PRECOMPILED LISTS
Freesound [1]!
[1] http://www.freesound.org/The Freesound Project is a collaborative database of Creative Commons licensed sounds. Freesound focusses only on sound, not songs. This is what sets freesound apart from other splendid libraries like ccMixter.
TurboSquid ( www.turbosquid.com [1]) contains quite a few free models and textures (there are also ones you have to pay for, although you can use the searching/sorting features to ignore these). It's the best collection I've seen, however, due to the different styles (anyone can upload models/textures) it is also inconsistent. There are a few other sites you can find with a few simple searches, however, these don't have the wider selection of available models. I believe the licensing (i.e. royalty free etc.) depends on the individual model in question - it is up to the modeller to decide.
[1] http://www.turbosquid.comSlayer, and OpenFrag artist package. It contains thousands of free textures, high quality. Good people at OpenFrag. ;) Download link to files hosted on sourceforge. [1]
old link [2]
[1] http://sourceforge.net/projects/openfrag/files/Artwork/Slayer%20texture%20pack/Not game-specific but you can find simple public domain vector art at http://www.clker.com/
For photographic materials I strongly recommend http://www.everystockphoto.com . It allows you to search through about 5 million photos and restrict the search to a particular free license type (eg, public domain, CC-BY-SA, etc...).
Wikipedia and Wikimedia commons (http://commons.wikimedia.org/) both have growing collections of CC/GPL image, video and audio.
In addition gnome, KDE, GTK, litestep and other window manager/decorators have numerous reusable desktop theme packs, which would provide useful UI elements.
You specified no art from commercial games but open-source games have a lot of GPL/CC'ed art. Notably Warzone2100 provides a rich collection of sci-fi vehicle and weapon models.
For space/sci-fi games the NASA website contains a MASSIVE collection of public-domain photos (nebulas, Mars, the moon, rockets, Earth (seen from space) etc...).
Free sprites:
There is for example the Open Clipart Library [1] (Public Domain Content). The german "MedienpƤdagogik Praxis-Blog" [2] has two nice collections/link lists of such "free content" websites. Altough the descriptions are in german, there should be no problem in following the links and land on mostly english pages: Music [3] and Pictures [4].
Alas, these are mostly CC.
[1] http://www.openclipart.org/Are you looking for content which you can distribute for resale? or just content which can be distributed in freeware? It's quite an important distinction!
Good places to find models which I use are:
http://www.gamasutraexchange.com/ (models, textures and software)
http://www.3d02.com/3d_model_index.aspx?LstType=5 (not free, but lots and lots of content if you're willing to spend a little on your hobby)
http://archive3d.net/ (free and lots of variety)
http://www.3dvia.com/index.php (free with lots of variety)
The only place I've seen for music is http://www.jamendo.com/en/albums which is very good, but you may not include any of this stuff if you intend to ever sell the game (given that it's a hobby project I guess not).
A big list of sound fx can be found here http://www.stonewashed.net/sfx.html
I think that's all the pertinent links I have lying around in my favourites ;)
I don't know much about it, but I've heard quite good things about ShareCG [1]. It seems to cover all the bases - models, textures, scripts, and a whole load of other crap.
[1] http://www.sharecg.com/There's a list on wiki.freegamedev.net/index.php/Free_3D_and_2D_art_and_audio_resources [1]
[1] http://wiki.freegamedev.net/index.php/Free%5F3D%5Fand%5F2D%5Fart%5Fand%5Faudio%5FresourcesFor music there is jamendo [1], I think you need to register witch is not very hard(free). The sites has only free music:cc. Tryad has some nice songs from there; there are others too...
There is a stock section on deviant [2] witch has pictures, textures and a few models. The stock things can generally be used, thats why it was put there.
[1] http://www.jamendo.comFor music, try opsound [1]. It has a large collection of music all of which is under a Creative Commons license. The site is also good if you just want some free music to listen to.
[1] http://www.opsound.org/index.phpGSArchives [1]
A massive collection of game sprites. They are extracted by original game so make sure you use them carefully. I would suggest only for testing or learning purposes.
PixelJoint [2]
This contains a collection of pixel art by various designers. If you look for the right keyword you may find some interesting sprites.
[1] http://www.gsarchives.netFor sounds I like http://www.mysoundfx.com
You can find Free Sprites [1] on hasgraphics.com. It features resources available from other sites that can be used in commercial and non-commercial projects.
[1] http://hasgraphics.com/free-sprites/