Killswitch Engage... I accidentally grabbed a CD that I thought was mine from the car of a friend, and it was full of songs of them. I went home, put the CD on my computer and... Well, since then I have loved that band. (In my opnion, at least)
Also, MLP: Friendship is Magic... but nothing that accidental, I just had nothing to do that day, and I clicked the episode in YouTube.
Finally, Dead Space... I hate scary games because they are... well, scary. But two weeks before the release of Dead Space 2, I wanted to buy a game (Can't remember which one) using Games on Demand in Xbox 360. Once I found it, I heard the sound of the doorbell. Before I went downstairs, I asked my sister to buy the selected game on the screen... what I didn't knew, was that when I threw the controller, the sticks moved the selected game to Dead Space, and my Sister tought that was the one I wanted... greatest mistake ever, because I loved both games (Dead Space 1 and 2)