I've got a Sega Master System 1 just for Sonic the Hedgehog, since I remember enjoying it a lot on a friend's Game Gear back in the day. Then, I realised that Sonic runs really slow on that PAL machine. (pun intended). So to speed the poor guy up, I yet need to perform a 50/60Hz mod.
One day, I'd like to get my hands on Micky Mouse: Land of Illusion, although I'm in no hurry.
Another friend gave me a Game Gear some years ago. He told me, he found it laying around somewhere, when he passed it on to me. Yeah, sure he did... I better not ask him twice about that.
I still have no game for it. Since many games are SMS conversions anyway, and I have no way of testing the hardware first before buying a game, I just leave it on the shelf.