DVDs: no real organization
Books: nonfiction on bottom shelf, misc. fiction on middle shelf, fantasy/sci-fi on highest shelf, collections (e.g. all 7 harry potter books) on top of the shelves
CDs: Sorted by genre, and alphabetically within genre, and alphabetically by album within artist/band.
CDs are most organized b/c I listen to them more often, so there's more of a need for them to be organized, so it's easier to find them.