Some Lego stuff, off the top of my head.
A 2001 Bionicle movie. Never formally announced, just alluded to by Templar Studios, who produced web content for Lego in the early 2000s. May have been scrapped because Lego was unsure about the franchise, so they held off on making a movie until 2003.
A Johnny Thunder animated series from around 2003, based on the Lego Adventurers toy line. Pitched by The Skong Works and Calibre Digital Pictures, rejected because Lego wasn't interested. Here's the animated pitch: https://www.youtube.com/watch?v=vPtORtgvIXw
A Bionicle Makuta origin film. Only mentioned in passing by composer Nathan Furst, probably one of the many ideas Lego played with for potential Bionicle movies.
A 2010 Bionicle movie with the Element Lords as villains, a sequel to 2009's The Legend Reborn that ended with a sequel-hook. Scrapped because Lego was putting the Bionicle line on hiatus.
A Hero Factory live action adaptation from 2012, to be produced by Universal and penned by the writers of Predators. This one was actually officially announced but canceled almost immediately, probably because Lego began working on the ill-fated Bionicle reboot around that time.