I just like good-quality, well-made documentaries, which would be worth buying and watching in their own right.
Bullitt SE for instance has 2 interesting documentaries, 1 about McQueen's career, and one about movie-editing.
I also like making-offs, when it's about martial arts movies. The most enjoyable for me is the Ong-Bak making off, which TBH is more impressive and fun than the actual movie.
Also, I like trailers, especially trailers of good movies, or just great quality trailers. Most of the trailers are pretty mediocre, but some are great, and TBH I feel they should always be included on a home-release.
I usually don't care much about the PR-marketing drible some movies put on there, like the Tom Cruise movies where everyone just tells about how fun and exciting the movie was to make, how everyone was great, that everything was amazing, blahblahblah. Those really insanely 'positive' 25 minutes informericals ...
I only enjoy those when I actually like the people talking, like Chris Rock, Jim Carrey, whatever. Just people that are ok with not playing along with the BS you're supposed to spit on these kinda deals.
On the Pixar DVDs, I always love the extra short animations. Just watched Rattatouile for the first time yesterday. Awesome flick, but the shorts were cool as well
And with Wall-E, comes Presto, which is one of the funniest shorts I've ever seen. Just brilliant. A great throwback to the old Bugs Bunny/Daffy Duck days, and I really wish Pixar would just start up a sub-section to make more of these kinds of shorts.
I dont care much for 'stills', or 'posters', or just pages with info you can scroll through and read. By all means, put HD images on the DVD/BR, cause they can always come in use when you want to make a cool background, or write a review, or whatever... but when I'm watching a DVD on a TV, I couldnt care less about that kinda stuff, unless it's an animated movies, so they're WIP/concept art stuff (and then, they need to include a proper 'browser' on that section of the disk.
Commentaries can be very informative and/or entertaining, but for alot of movie I dont really bother with them.