Excluding the Pokemon games, I enjoy playing lots of old Genesis / Mega Drive games every once and a while. People don't understand how I could play games that weren't on the new consoles, but I like most of these games for the nostalgia factor.
Mine's similar. I can't dare say pokemon now at 25 to anyone, so I keep that to myself.
My main one though is my N64, which I still have. Now and then, a good crack on Conker's Bad Fur Day or WWF No Mercy is what's needed. I have the Sonic Classic Collection for the DS as well, which I love playing quite often for a quick runthrough.