I actually redo all the spines on my cases to reflect what's in them--unless it's just too many titles. If so, then it is usually overlaid on the back cover at least.
I also keep a notebook that I divided into alphabetical chapters of about 10 pages each, more or less.. Everytime I buy a new dvd/blu-ray it is written down in it's respective section. Whenever I want to watch a movie I just pull out the notebook and browse. Saves me having to stare at the bookshelves with my head turned sideways for forever trying to decide on what to watch.