Can someone please suggest to me some good sites where I can download a variety of sound effects or from?

I've recently taken up freelance video designing (Adobe Aftereffects/MAXON 4D/Blender etc) , & am engaged in designing videos for miscellaneous employers, such as a few NGOs in my area for whom I am designing video promos to launch their programs/initiatives, as well as some soccer fansites, for whom I am designing season highlight packages, & sometimes promos or vignettes for the upcoming new season. I'm also designing a video for a regional MMA wrestling type company. I basically need suggestion of sites which might contain a large variety of background or foreground SOUND EFFECTS, or BACKGROUND-TYPE MUSIC, or THEME MUSIC for my videos. Any help will be greatly appreciated. :)