Shields Library, UC-Davis, 2007.
http://www.youtube.com/watch?v=Vd4DicoDiCk
See also http://www.youtube.com/watch?v=tkIRWoo9qrU at Brown University.

Unshelved, online comic by Bill Barnes and Gene Ambaum (previously known as Overdue), also available in book form.

Shelf Check, online-only comic by Emily Lloyd. My favorite. So funny and subversive.

Late addition: there’s also James Turner’s Rex Libris series. Rex Libris, a former Egyptian god, is the Head Librarian at the Middleton Public Library.

Common Misconceptions about the Eden Prairie Library. Eden Praire Library, Hennepin County, Minneapolis, 2007. A level 27 warlock in the library?
http://www.youtube.com/watch?v=mi78YJ1CD4Y (Thanks, Emily Lloyd!)

Pac-Man reenacted by humans.
UGLi (Undergraduate Library), University of Michigan, 2005.
http://www.boingboing.net/2005/12/21/pac-man-reenacted-by.html
http://www.youtube.com/watch?v=0FGzOoVvo6w (Thanks, BoingBoing!)

Denver Public Library, 2007. Includes riding on book trucks, making book angels, and reading books. http://www.youtube.com/watch?v=tFDo1dt0_Lo

Hennepin County Library, Minneapolis, 2007.
Emily Lloyd’s blog

Second Life Libraries, 2006.
http://www.youtube.com/watch?v=jTQkzfz5osQ
(A virtual shenanigan.)

Lest the Keepers of the Book Wreak a Terrible Vengeance.
Boulder Public Library, 2007. Pro-librarian conversation.
Overheard in the Office Also: http://www.overheardintheoffice.com/archives/005029.html (and all librarians can tell you about unusual things used as bookmarks, like condom advertisements or strips of bacon.)

From Weird Al Yankovic’s UHF, 1989. http://www.youtube.com/watch?v=mZHoHaAYHq8& (A fictional shenanigan.)

Extended computer start-up sound from prangstgrüp.
Columbia University library?, 2005.
http://www.ronniedelcarmen.com/blog1/2005/10/prangstgrup-videos-if-laptop-startup.html
http://www.youtube.com/watch?v=Mt1bgsvsWms