For a limited time, Blasterware fx is offering a free download of 68 high quality sound effects. There is a good variety of sounds in the back so you might want to check it out. Actually, since its free you should get it anyway, you can never have too many sounds effects!

Found out about this on the users group Final Cut Montreal (French).

Link: http://www.blastwavefx.com/i25/Blastwave-FX-Free-Sound-Effects-Download-Pack/information.html

If you want to add some music to your clip, go take a look at ccMixter. All songs/remix are available under the creative common attribution-noncommercial  license which means they are free if:

• you are not making a commercial use of the song
• you identify the source. 

Before using these sound clips, read the license and make sure you are making the right choice for your project.