Sonic Adventure 2 - City Escape (my little sister can still sing every word to the theme song, and she's NOT a gamer.)
Goldeneye - Facility (more battles there than any where else, and the music was epic)
Bubble Bobble - Level 25 (The Popcorn Level. Always felt like we'd achieved something as kids when we got there!)
Jumpman Jr. - Figurit's Revenge (If you've never played Jumpman Jr., you should really watch a video of that level. Evilly awesome.)
Super Mario RPG - Tadpole Pond (Organizing the tadpoles for music notes is one of my favorite parts in the game. Also the animation of Toadofsky when you actually get it.)
Earthbound - Magicant (Such a fantastic trippy level. Also I love the Flying Men. And in the Japanese version, your character is wandering the map naked, which gets points too.)