Oh, I forgot to mention another free hosting site I'm aware of.
Microtech File & Avatar Hosting
was pretty darn reliable when I was using it (as of last week!
) The only thing that might be considered a downside is that you don't actually sign up, so there's no account to manage--if you forget your URL, you might have to upload it again. (There is an option that emails you the link, however.)
Hope this helps!