Atari Games Online!
Super Mario was a pretty big part of my life back in the day. Nintendo was the last time you could call me a "gamer". I was too poor for a Game Boy and there was no way my parents were buying me a Sega with a perfectly good NES and functional Atari system under our roof.
I remember when we first got our Atari. My parents stayed up until 3 in the morning playing Pac-Man and my sister and I would take turns playing while the other one would chant "Die Sucker Die, Die Sucker Die". Good wholesome chanting, the whole family can follow along with.
Atari still works, by the way...which brings me to this:
Have you seen this? You can play every (I think) Atari game ever, right here in your browser! If you're reading this on a mobile site, than you can download Atari's Greatest Hits for iPhone or Android.