I've just checked the starwars.com comparison list for Empire and it seems they did a really good job on that one. The only things not listed that I know of is the A long time ago in a galaxy far, far away.... text and a minor special-fx correction done to the "Space Slug scene," in the original film when the space slug comes out of the asteroid to reach out after the Falcon, you can see the whole asteroid bounces a little at the end of it.

The funny thing is, if you don't count the added scenes in the SE to the trilogy, The Empire Strikes Back is the most altered film of the three, it's just that the changes happens to be more subtle and tastefully done.