For me it was the Quick Look of the Xbox 360 version of Borderlands. On another site someone posted the link to the Quick Look and, at the time, it was the longest gameplay footage of the game, so of course I checked it out. I liked the style how they handled to show the game and the personalities in general. After that video, I went to this site and watched the other Quick Looks, started to differentiate the guys from each other, listened to the latest bombcast and little by little I was consumed by GB.
P.S.: Congratulations for me for my first thread.