Being an indie developer is fun, but sometimes it can be frustrating when you can't get good sound effects! Now, don't let your games go quiet just because you can't afford a sound artist or get that tune just right! I've thrown together a list of sites that offer quality music and sound effects for public domain*. I'll update this list as I find more and feel free to suggest a site!
Info: Freesound is an excellent website to find free ambiance tracks or sound effects for just about anything you could need. Unfortunately there isn't much of a variety of musical pieces but Freesound is still one of the best options for getting public domain sound effects!
Info: Jewelbeat is my go-to website for professional musical tracks ranging from classical, to metal and everything in between. They're not free, but all of the audio tracks they have are only 99 cents which is an incredible deal for such professional 2:00 - 5:00 minute tracks! Definitely a tier one site for audio assets!
Partners In Rhyme
Info: While far from the best and with a limited catalog, Partners in Rhyme has a handful of great sound effects that would work great in most BYOND games!
Info: SFXR is a program that easily generates sounds that the user can easily reject or accept and alter to fit their needs! *thanks to LordAndrew.
Info: Although not much of a program for making sounds, it's probably the best free program for editing sounds and audio files. Between fixing clipping, changing pitch, panning or even just changing the audio format, Audacity is your best bet for editing. Definitely a personal favorite!
Info:BFXR is like an improved version of SFXR(see above) that generates sounds based on the input parameters! Don't want to download anything? No problem! There is a browser-based version of the program embedded on the homepage! *thanks to FIREking.
Info: A great website full of tracks that you can search through with a clever search system that you can select the atmosphere, setting, and intended use of the music. Did I mention it's all free?
* -Public domain; Open for public use so long as credit is given to the original designer.