I'm not an expert on these sorts of things, so I’ll have to take the word of Eurogamer when they call an eBay auction that sold for a whopping $1.32 million the "biggest game collection" in the world. We'll leave that determination to the officials at the Guinness Book of World Records...
But the collection can at least be called massive: It featured thousands of games including every title ever made for a Sega platform - the Saturn, Megadrive, Master System, Game Gear and Dreamcast. It also included every game ever released for a Nintendo platform, to the GameCube - NES, SNES, Virtual Boy, N64, N64 DD, and Game Boy. Many of the games were sealed in their original shrink-wrap and some were titles that were never sold at retail and ultra rare.
You can check out the eBay auction listing here. The image in this story comes from that eBay listing.