I have further designs to add:
North American Sega CD/Saturn cases: A hybrid DVD case and jewelcase. In other words, take the basic components of a jewelcase and expand them to DVD-case dimensions. The result is a huge piece of crap that won't fit into any existing rack for any sort of media, plus the extra large plastic face is weak and prone to cracking. Still, it allows for a decent sized manual, and also has facility for a second plate for multiple CD games, like Ground Zero Texas.
European Playstation (and some Japanese) Playstation cases: A mutant jewelcase, but not quite as large as as a 2-to-4 double case. Holds the CD in place and allows for a title slip seperate from the manual. Unfortunately, the manual is not held in by anything and tends to fall about annoyingly until it is lost.
European Dreamcast cases: A further evolution of the idiotic Euro Playstation cases above, these are the same basic size and shape but with far more moving parts. These feature two flaps around a central piece, so they could theoretically support four CDs (or should I say, GD-ROMs). The front compartment is meant for the CD, while the back for the manuals and such. This works well until you notice the back liner slip isn't held in, and opening the back compartment will result in it probably coming loose and then being smushed when you close the case again. Nicely robust, though.
What baffles me is that for the North American Dreamcast and Playstation, and Japanese Saturn releases, normal jewelcases were adequate. Europe is already cursed with PAL conversions of games, why force these poorly designed muto-cases on us?
Update 29/10/2004: Gunghir suggests the bizarre cases are to accomodate the several European languages you get with PAL games. I can see the value in this, my Canadian copy of Jet Grind Radio had to have the legally-required French manual shrinkwrapped to the back of the CD case. However, living in Europe for a long time now I've noticed bizarre things about which languages are included - I've had English, Finnish and Swedish (for a hockey game), English, Spanish and Portugese (for a strategy game). It must be galling, though, to be Danish or whathaveyou (one of the 'less popular' European languages when it comes to games translation) and turn past the English, French and German to find a single page telling you to look on the game CD for a PDF of your language's instructions.