Stock Footage for Free is a decent site that delivers exactly what it sounds like. Everything is royalty free and monetarily free (you do have to register, however). They have some stuff in HD, as well as a lot in SD. While the selection isn't perfect, hey, it's free. It's great for certain cityscape or wilderness shots, and they even have some time lapses and stuff. It can be great for the starving student who needs that establishing shot, but can't shoot or pay for it.