Emulators are a great tool for nostalgic gaming, but what if you want to see all your favorite games of the past improved a bit. Wouldn't it be great if somebody out there lived the same old video games you did and created updated versions of them? It turns out, a lot of people are doing exactly that, and here's an index of many of these projects:
http://remakes.org/
Do you fondly remember Intellevision's Night Stalker, now there is Afternoon Stalker. Think you're the only person who ever loved Rampart? Think again, there are two remakes. You might even discover things you never knew existed.
I never had a C64, so I never knew about The Sword of Fargoal. But the remake is fantastic. It seems like just a very simple Rogue-like game. Once you start playing it though, the elegance of the game design will continue to surprise you. Granted, you could just play the original on an emulator, but when you turn on the optional enhanced graphics and read over the game play modifiers, you realize this is truly an evolution and not just a remake.
Plus, if you are going to just check out an emulator for a system you never owned, you pretty much have to rely on trial and error to find the great games. All of these remakes are games people loved enough to copy and enhance! Most of them are freeware or shareware, so go have a nostalgic day.