I am not sure if I want to get the Mission Impossible III Blu-ray disc as I already own the same movie in SD version. Is there a forum that list which DVDs would be best suited for Blu-ray in terms of sound and video vs SD DVD?

http://www.dvdtalk.com/reviews/hd.php

A minority of reviews/reviewers might offer a little tidbit on how an HD release compares to a previous SD one but it is entirely dependent on whether they have access to the SD. Check reviews using something like DVD-Basen.

What titles that are going to interest you to rebuy are likely going to be an individual decision based on your enjoyment of the film. HD releases will almost always offer greater color accuracy, contrast, sharpness/detail. Check reviews on a case by case basis and decide from there.

Some people have this idea that only action and sci-fi epics are "suited" for HD, and that a dialogue-driven movie like a comedy or drama, or an older movie isn't worth it. While it's true that discs vary in quality (with the source often being the determining factor), I feel that any film can benefit.

So naturally, I'm going to say it's worth it, but even if you happen to have feelings about what "belongs" on HD and what doesn't, it's still worth it. After all, it is a very recent action movie and it's gotten very good reviews. Plus, there are some extras in HD.