SFX, Video & Foley Libraries
Soundbible
SoundBible offers thousands of free sound effects, sound clips, and straight up sounds. These sounds can be used in a variety of sound projects including Video Sound Scores, Movie Scoring, Game Design, Powerpoint Presentations, Prank Calls, Sound Boards, and the list goes on. SoundBible.com is a great source for copyright free sounds.
Freesound
Freesound is a collaborative database of Creative Commons Licensed sounds. Browse, download and share sounds. It is free, but they do accept, and encourage, donations.
Audiomicro
You must create an account, but no payment info is required. They have a decent list of free sounds available. More extensive content is available for purchase.
Internet Archive
The Internet Archive, a 501(c)(3) non-profit, is building a digital library of Internet sites and other cultural artifacts in digital form. Like a paper library, we provide free access to researchers, historians, scholars, the print disabled, and the general public. Our mission is to provide Universal Access to All Knowledge.
Noise For Fun
A clunky interface, but it is free and does not require an account.