Star Wars, Empire and Jedi, all on the official site.
IIRC audio changes are not covered though.
Alternatively you could check this article on Wikipedia, 'cannot say how reliable it is.
Mod Edit: Unfortunately some of the articles linked to above no longer work. However, the Internet Archive’s WayBack Machine has a working functioning link for them, here:-
with doubleofive’s re-upload and compiling of them, here:-
StarWars•com Official 2004 Changes Preservation : SW : ESB : ROTJ