Good, safe site. Hosts free sound files, both free as in freedom and free as in lunch, and uses Creative Commons licenses to ensure that work does not get abused.
Brilliant if you need free sound effects for school projects, online videos, or if you are working on an indie game. Nobody should have to pay for sound effects. Its a wonderful project and I enjoy sharing my own recordings there too.
Especially if you are a Flash developer, this website gives free user-submitted sound effects or non-copyrighted music for one to download. So far, I haven't had any virus problems.