On Internet there are many ways to find music and sounds for your game.
I am going to suggest you few sites that I think are interesting, but first of all take always in count that the more music and sounds you add the more your game size will increase.

Because of this it is always better to find loopable music not longer than enough... for example you should get a 10-15 seconds loop for the menu and a longer loop, 50 to 70 seconds for the game.

It is usually better to choose WAV files because they can be compressed from a good starting point, sometimes MP3 are already compressed too low. About compression is important to change something in File->Publish Settings..., just make sure you set everything to the right Bit rate, for me the right compromise is a 64 kbps stereo, compressed at best quality, but I suggest you to tweak it and test to see if you like any other setting, just don't go to low or the music will sound very choppy.



Good sound and music can only compliment your game, pushing it to the next level of polish. The issue is that a game that isn't very fun will not become more fun with great sound considerations (unless the game itself is based completely around the music and sound).[...] Click here to read more...

Sonoflash in amazing, you can basically add sounds to your flash games just writing some code, and the sounds will be distorted and changed however you want.

You can choose from a list they provide on theire site and download, for free, the sound that you need.

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