Been in a retro mood of late so; Mega-Lo-Mania, Cannon Fodder, Speedball 2, James Pond, Magic Pockets, Gods, Micro Machines, Paperboy, Turrican II, Worms, Zool and Rainbow Islands.
Worms for sure! Monkey Island - the classic! Of the newer ones? Uhm. Trackmania Nations make me smile, but then again - it can also make me pull my hair in frustration while smacking my forhead against my desk. So...
Good games, though I've found that the best 3D version of Speedball 2 is Deadthrow on the Xbox. Its pretty much exactly like the original with a few rule modifications. If you ever have the opportunity to try it you should.
pop'n twinbee. whenever i think of it, i instantly think of the first level music. and my childhood. although, that said, there's a ton of super nintendo and mega drive games i could mention that make me "smile" and think of awesome times. i won't bother mentioning them unless pressed -- the only reason i mentioned pop'n was the fact that it was the first game i thought of, heh.