Seriously, get a CD Binder, they're awesome at holding old game discs and the sort... organized, tidy and far far less space.
The other thing I do - is if it has manuals and stuff, I'll flatten-out a game box (if it's cardboard) and stuff multiple jewel cases within another retail game-box. Usually, I do that for a game series.
-> I have my old Diablo 1 jewel-case sitting there within Diablo 2 retail game-box. It fits.
Another thing I do - is I'll take those plastic cases that give me enough room and ain't got enough discs sitting on its CD-pole, and put multiple game series or versions within that box and on the pole.
-> I have Fable TLC Retail Box. It has like 4 CD's. I also have a Steam-version, which I cut onto one DVD and put that on the pole.
-> I have Res Evil 4 PC retail box. It has a bunch of CD's on its pole. I also put my Steam back-up folder of RE5 on a few DVD's on that pole.
-> I have Retail copies of STALKER: SOC + Clear Sky. SOC came in a nice DVD retail box case w/ multiple discs on a pole, while Clear Sky's just came in a slim DVD case w/ room to put one disc on its pole. I put Clear Sky DVD in the SOC box. I pulled the Clear Sky cover off its cases and used that blank slim DVD case for some other 1 DVD-disc game.
Also, sometimes - the game-cases I have, they have an empty place in the jewel case. I'll put more discs there.
-> Retail copies of Vampire: Bloodlines comes in a quadruple CD jewel-case. Game came w/ 3 CD's, while 4th slot is completely EMPTY. I filled that case - I cut a disc there w/ a fair deal of data in there (patches, unofficial patches, save files from multiple play-throughs, etc).