Here is a collection of websites to find free sounds for your game.
FreeSound
FreeSound.org has a large database of sounds that are licensed under Creative Commons. This makes it really easy to see which sounds you can do anything with, which ones you have to attribute and which ones you can’t sell in a commercial product. For home or personal use, you can pretty much use any sound on the site.
You can search sounds or browse by tags, geotags, or packs. I really like the packs feature because you can find a bunch of similar sounds quickly because they are all grouped into a pack. You can preview the sounds, but have to login in order to download.
AudioMicro
AudioMicro.com has about 2,000 free sound effects that I found to be of good quality. They have a lot of other sound effects, but you have to pay for those. It’s not a whole lot of sounds, but it’s a decent database nonetheless. You do have to login in order to download the original sound file.
FreeSFX
freeSFX has several thousand free sound effects that are also of very good quality. They also have hundreds of categories, so it’s pretty easy to find the exact type of sound you are looking for. Unfortunately, the search box on the site produces an error, so you can really only browse via the categories.
SoundBible
SoundBible.com has about 2,000 free sounds that are licensed under Creative Commons. If you want to use a sound effect that will be for commercial purposes, you can click on royalty-free sounds. This is one of the few websites where you can download the sounds without having to create an account or login.
PacDV
PacDV is a small business site with a few hundred high quality sounds added for their clients. They have a couple of interesting categories like machines, mechanical, and interfaces. On this site, you have to right-click on the link and choose Save Link As in order to download the audio file.
Flash Kit Sound FX
Flash Kit Sound FX has several thousand sound effects for flash developers. Luckily, anyone can download them without needing to register or login. Also, on this site, you have to right-click on the download link and choose Save Link As in order to download the MP3 file.
GRSites
GRSites has a couple of hundred simple sound effects that you can download for free and without registration. All sounds are free for personal use. If you need any sounds effects for commercial use, you have to purchase the commercial license.
SoundJay
SoundJay has few hundred sounds that are completely free and can be downloaded without any need to login. The files are good quality also, mostly 16-bit stereo 44.1 kHz or 48 kHz.
SoundGator
SoundGator is another site with a decent number of good quality free sounds. You do have to register and login in order to download the files. The site probably has a couple of hundred sounds.
99Sounds
99Sounds is a cool site because it has a bunch of collections of high quality sounds created by various sound designers. The collections are quite large and the audio quality is superb.
(original post by Aseem Kishore)