Suikoden 2, $20 at a flea market brand new. Didn't know much about it at the time, but one of my friends loved the first game, which I thought looked and sounded kinda strange. We swapped the games - he was blown away at how good #2 was, and I was surprised at how much I enjoyed #1. I ended up joining a goofy online fan community based on #2, I became so enamored with it.

CoD4 my dad gave me a bunch of vouchers he found in a drawer when I was heading out to get Ratchet and Clank, decided to get CoD4 with the vouchers. Didn't touch Ratchet and Clank for months.

For me, Fire Emblem: Awakening.

I bought that game for no real reason, only to end up enjoying it thoroughly.

South Park: The Stuck of Truth. I had never even seen the show but the cover looked cool and it was on sale so why not.

Same here. Saw it on sale for like 60% off on Xbox, figured what the hell. One of the best games I've played all gen so far. Damn good

Dark Souls.

Definitively one of the best thing that ever happened me in my gaming life.

Runner-up is definitively Dragon's Dogma, which incidentally it is another of the best things that ever happened me during the seventh generation.

In recent memory (as in, 7th gen and newer), I'd say probably Professr Layton and Pandora's Box.

7 days to die.
got drunk, wanted a zombie game, the alpha was on sale. well the game is getting better with every update, it looks realy nice since last patch, it runs well, the random world creator is realy nice(now, was not that great when they patched it in, the world was not that well created). hope they patch some of the assets, but its getting there and it plays so well

Shovel Knight. It was on sale and i had heard that it was awesome. It was.

Just Cause 2