Nightmare dates all the way back to 1980. Burton worked on Fox and the Hound and the Black Cauldron and then started working on his own animations such as Frankenweenie and Vincent - Nightmare was in that group of projects he worked on.
By popular demand, a bullet about Henry Selick. Selick was, in fact, the director of Nightmare. Due to his prior commitments to Batman Returns, Burton wasn't able to spend as much time on set as he would have liked and hired newbie director (although industry veteran) Henry Selick to do the job. The movie was (and still is) billed as Tim Burton's The Nightmare Before Christmas because studio heads were convinced that the movie wasn't going to do well, but attaching Burton's name to it might give it a better chance at the box office. You might know Selick's from his latest amazing stop-motion picture, Coraline, which he also directed.
You know the voices of the characters; you just don't know you do (or maybe you do). Jack's speaking voice is done by Chris Sarandon, who is Prince Humperdinck in The Princess Bride. Sally is voiced by the legendary Catherine O'Hara, who has been in everything from SCTV to Home Alone and Christopher Guest's mockumentaries Waiting for Guffman, Best in Show and A Mighty Wind. If Dr. Finklestein sounds familiar, I bet you're also a National Lampoon's Christmas Vacation fan: he was the cigar-smoking, toupee-wearing Uncle Lewis. The Mayor of Halloween Town is voiced by Glenn Shadix, Otho from Beetlejuice, and if you listen closely, you'll notice that Lock is voiced by Pee Wee himself - Paul Reubens.
Tim Burton has said that Jack Skellington is one of his favorite characters largely because he so deludes himself into thinking that he's going something wonderful and great without thinking about how his actions would impact others.
Jack Skellington has cameos in other Burton movies and Selick movies, if you've got eagle eyes . In Beetlejuice, his head is on top of Beetlejuice's carnival-type hat near the end of the movie, and in James, he can be spotted as one of the pirate skeletons James comes across.
Danny Elfman says the composing songs for this movie is the easiest job he has ever had. This was news to me - he used to be in the band Oingo Boingo. At the time Nightmare came around, the members of Oingo Boingo were starting to go their separate ways; he wasn't sure what was going to come next. Reflecting this, he simply wrote Halloweentown songs as if they represented Oingo Boingo - the past and what he had always known - vs. Christmastown, which was new and fresh and exciting.
The NAACP became upset with the makers of the movie because they felt that the movie's chief villain, Oogie Boogie, was made to use "blackspeak" while the heroes of the film used "whitespeak." Director Henry Selick and composer Danny Elfman say that it had nothing to do with race; they had simply based his singing voice on Cab Calloway because they liked the style and tonal quality. I, for one, am inclined to believe them - Danny Elfman has been influenced by Cab Calloway since his Oingo Boingo days when the band was doing covers of his songs.
Oogie Boogie used to look a lot different. Burton's original drawings portrayed him as a pillow-sized baddie, which wasn't too intimidating. When they upgraded him to a larger-than-life sack o' bugs, suddenly a lot more bugs were needed in order to animate the scene where he unravels and all of his insects come pouring out. So, any time anyone had any downtime on set, they were tasked with making a bunch of Oogie bugs to use for that scene.
Greg Proops from Whose Line is it Anyway? voices a bunch of minor characters in the movie - the sax player in the band, a red devil and the harlequin demon among them.
There was talk of a sequel for a while. Obviously it has been quite the cash cow for Disney, so around 2001 they started buzzing about making a computer-animated sequel. Tim Burton managed to talk them out of it, saying that it was really best the way it was and "Jack visits Thanksgivingworld" or something similar just wouldn't have the same impact and would also cheapen the first film.
Just as Jack shows up in other Burton movies, other Burton movies show up in Nightmare. A cat from Vincent can be seen in the beginning knocking over a trash can; the snake in the movie looks suspiciously like the Sandworms from Beetlejuice; one of the toys Jack hands out is an evil duck on wheels which is just like the Penguin's vehicle of choice in Batman Returns.
Vincent Price was originally slated to be the voice of Sandy Claws. Unfortunately, Vincent had just lost his wife and had a very sad quality to his voice that wouldn't read right during his recording. They ended up not using him and he died not too long afterward.
Tim Burton has said that he felt a little subversive in designing the Nightmare characters the way he did. Coming from Disney, he had to draw the big "wet drippy eyes" that Disney characters are famous for. Quite a few of the characters in Nightmare either have big black voids for eyes, like Jack does, or have eyes that are sewn shut or are otherwise mangled. Burton said that not having eyes to convey emotion and expression was challenging and felt that if they would be able to accomplish emotive characters without eyes, it would be a real achievement.
The Haunted Mansion at Disneyland has transformed into Haunted Mansion Holiday featuring Jack and Sally every year since 2001. I've yet to see this for myself, but I hope to someday soon - the pictures look amazing.
Photo from DoomBuggies.com.