Okay, new topic and with an old school flavor. Name your favorite game for any system you want. You can list multiple systems but only one game per system.
So, pick you favorites. To get things started I'll go with the Atari 2600 and Dreamcast first as they were easy choices for me. Also, no arguing as each of these are just opinions and there will always be games that are in other genres you might like better.
Atari 2600 - Riverraid
I can remember my dad and I trying to get a little further each time but never succeeding in making it all the way to the end. Not even sure if there was an end. A fantastic experience of balance versus reward in upping your score by shooting the fuel at the last second or sucking it up completely to fly a bit further.
Dreamcast - Soul Caliber
Hands down my roommates and I during college/shortly after have spent more time with this game on this console than any other. The sequel 5 years later was a minor graphical update which only goes to show how awesome the original was.