Metal Gear, Dragon Quest, Final Fantasy, formerly Grand Theft Auto and I suppose now Call of Duty.

I bought my PSP for MGS: Peace Walker. My PS3 for MGS4. My Nintendo DS for Final Fantasy III. I actually bought my new laptop to coincide with Diablo III, but I wouldn't necessarily say I bought it for it.

Whichever handheld releases a FF/DQ first dictates when I'll buy a 3DS/Vita. And I would probably buy a next-gen console at launch for whateve year's Call of Duty is sure to come out on it.