I'm sure most if not all of us have at one point or another sold, traded or gave away some item or items of video gaming goodness that we regret horribly now. Some of my regrets...
My N64 and games collection. I owned a pristine condition, original N64 with two extra controllers (grey) as well as over 24 complete, boxed, mint condition games. Even though I was never a fan of the N64, it was a very nice collection. Zelda Ocarina & Majora's Mask. Super Mario 64, Super Smash Bros., Rayman 2, Banjo Kazooie & Tooie, Starfox with the rumble pak, GoldenEye 007, Perfect Dark...a lot of highly sought-after titles. Traded it all in on an original Xbox and six games. I enjoyed the Xbox, but in hindsight I would have been better off keeping the N64.