That's a complicated question for me:
1. Sega Genesis games are in a tape case that's on display, mounted on the wall.
2. PS1 games are in a CD-tower.
3. Dreamcast games are on display in a wall-mounted CD case.
4. All of my NES & SNES games are on a 3-tier bookshelf.
5. All of my PS2 games are on another 3-tier bookshelf.
6. And all of my other DVD-sized games (XBox, 360, XBone, GameCube, Wii, Wii U) are on yet another bookshelf.
7. My Game Boy, GBC, & GBA games are in binders in 9-pocket trading card plastic pages.
8. And finally, my DS & 3DS games are in those 18-game holders that you used to get from Club Nintendo that are the same size as normal game cases, with the game's original cases on display on a bookshelf.