Metroid Prime: This is still my favorite game on anything. Combat, exploration, and the perfect atmosphere set by the music and graphics
SSBM: Six friends, four controllers, hours of fun every friday.
Mario Kart Double Dash: Above.
Soul Calibur 2: This game brought about as much real world fighting as there was ingame.
Luigi's Mansion/Mario Sunshine: Sunshine might still be my favorite Mario Game even with Galaxy II/SMW around.