There is an article on The Cutting Room Floor (Which is a wiki for documenting unused stuff in video games) for New Super Mario Bros., which I have added some things to. I also have made a list of all the unused stuff in NSMB I know about that is not in the article
here: http://tcrf.net/User:Hiccup.

Does anybody know any unused things that are not on the article or the list?
Maybe just more details on things that are already known or completely new things.

EDIT:
You can also just sign up to the wiki and add things directly to the article.

EDIT2:
I have added unused objects AKA sprites to TCRF

EDIT3:
I have added unused sprite data to TCRF
Have I missed any object/sprites or sprite data?

An unused object list would be nice too.
I wonder, what happened to the videos that you made a long time ago that showed the unused sprites? I remember they were there on TCRF. Also, unused behaviors could be added too.
_________________________

Unused objects and sprite behavour are on my list.
I never knew that the videos were on TCRF, they must have been deleted - they had bad framerate and anotations and they didn't have all the sprites and objects.
I can make videos in Desumenu now so when all the sprites, sprite data/behavour and objects are on the wiki, I will make a video of them and upload it to youtube+ embed on the article. I will also make better anontations. I will be making videos of all the unused levels as well.

It would also be nice if you could somehow rip the graphics of the unused objects. I remember the unused sprite 255 (the foreground plants) were added there. They could easily be ripped using the editor.
And a better video sounds good too. Used to show how sprites behave.
_________________________

I can't upload images to the wiki right now: http://tinyurl.com/d44kq9t

It would be helpful for the article if somebody made (high quality desemenu or ds capture) images for the unused sprites and unused sprite data. I won't be able to make them soon. I will give the person credit in the article. The unused tiles and other unused backgrounds would also be good.

@Dirbaio are you going to make the video with unused sprites with more stuff that you said you would?

Does anybody know about or how to play/view the unused wrecking crew minigame?

Hm, I never said I was going to make a video
I said I'd look at the code to see if there's something interesting (And no, I haven't found anything, but that's because there's lots of code to read)

Not recently - but you did on Jul. (cutting room floor/nsmb stuff/) or somewhere.