There are plenty that bring me back to the good old days, but two in particular have a substantial effect on me when I play them...
Mike Tyson's Punch-Out and Pitfall!
Pitfall! was the first game to really enthrall me, even though I was quite young at the time.
Mike Tyson's Punch-Out was the game that made me HAVE to have a NES. I'd say it has a larger "back in the day"-effect on me than even Pitfall!. The best Christmas me and my brother ever had was when we received our NES with the SMB/Duck Hunt pack-in, along with Mike Tyson's Punch-Out, Winter Games, Gun.Smoke, and Jaws.
"I feel like I could take on the whole Empire myself."