This is my new favorite special feature after picking up Zodiac 2-Disc Directors Cut.

I also remember Hollywoodland and From Hell having such documentaries on them.

Can you guys recommend anymore?

The Ed Gein doc on The Texas Chainsaw Massacre: 2-Disc set (remake) and the WADD documentary bonus disc that comes with Wonderland are pretty good

I said Hollywoodland but meant Wonderland. Also I totally forgot about that TCM one, I don't think I ever even looked at the Special Features on that one aside from the commentary.

in the old bruce lee box set (the black one) it had a good doc on bruce and his life.

Absolutely Agreed!

Can anyone else think of some more?

I also recall R2-D2: Beneath the Dome being fairly entertaining (although it's a mocumentary)

the documentary about editing thats on the Bullitt 2 disc

Auto Focus has one also

Pretty much every major release from The Criterion Collection

The Docu on the Tales from the Crypt Season 1 about the comic series was really interesting.

TAXI DRIVER had a bunch of special feature docs on it. They couldn't all have been "making of." I don't have it handy now or I'd check and see what they were.

Black Hawk Down SE 3 disc has a making of ,(which is great BTW), But also has a great historical documentary on the events as well.

Casablanca 3 disc has an interesting docu about Jack Warner (of Warner Bros).

(Some vague memories on some of these)

Malcolm X-Oscar-nominated 70's documentary
Enter The Dragon-Bruce Lee: A Warrior's Journey (It's more about Game of Death than Enter The Dragon)
Ed Wood-Featurette about The Theremin
Evil Dead-Fanalysis
Sunset Blvd-Edith Head: The Paramount Years
American Psycho-I seem to remember some sort of 80's documentary on this
World Trade Center-Documentary with Oliver Stone touring around NY sharing youthful memories
Glory-Voices of Glory
Schindler's List-Voices from the List
Once Upon a Time in The West-Railroad documentary
The Good,The Bad,and The Ugly-Civil War documentary
King of New York-One documentary is about Schooly D. The other has Ferrara's co-filmmakers reminiscing about working with him on his earlier projects.

And now for the oddities:

Reefer Madness-Grandpa's Marijuana Handbook
Eraserhead-Eraserhead Stories (Even though I don't remember a whole lot of Eraserhead being discussed)
Some of Something Weird Video's drugsploitation DVDs often include vintage drug documentaries

American in Paris: Gene Kelly bio
Easter Parade: Judy Garland American Masters
Singin' in the Rain: the Freed Unit

May not quite count, but I always liked the "Why Widescreen?" feature on the Die Hard Five-Star set. I wish more people had watched that rather than complaining about black bars.

Blood Diamond 2-Disc has a docu about the black market diamond trade.

A few years ago Biography episodes started appearing as bonus features. I think the Jane Seymour one appeared on Dr Quinn, and I think there were others.

If I remember correctly, 'V For Vendetta' has a mini doc on the origins of Bonfire Night in the UK.

MGM's DVD (and Blu-ray, I think) of DePalma's Carrie has a nifty little doc on the legendarily bad 1988 Broadway show Carrie: The Musical!