Basically, for their unforgettable N64 gems (I would've dropped the N64 without them) and DKC.
Donkey Kong Country Trilogy: Screw the haters, I love the series. Amazing graphics, music, and especially art and environments. DKC2 was the best, especially with the moody atmosphere. Seriously, why isn't there a Mario level that takes place on a haunted roller coaster, or a beehive?
Diddy Kong Racing: Brilliant racer. I can't even call it a kart racer, since you drive cars, hoverboats, and planes instead of karts themselves. The idea of 3 veichles and an overworld was really neat, better than MK64 in some areas. It's pretty cool how the Mario/Donkey Kong series technically crossovers into Banjo and Conker.
Banjo-Kazooie: The original was the best 3D platformer ever, IMO. Brilliant characters, music, humor, levels and design. Truly magical. I also liked the sequel, but it lacked the charm of the original.
Conker's Bad Fur Day: You really had to play this in early 2001 to appreciate this game. Pushed the N64 to its limit in all areas, and a great swan song for the system. Outstanding graphics and animation, voice acting throughout the whole game (a rare for N64's cartridge) great music score, and the twists at the end I didn't see coming.
Goldeneye: My first owned FPS, played the hell out of this game (both single and multi), and still one of my all-time favorites. Played a bit over the summer, I think it still holds up. Some of the best FPS level design too.
I liked a few others, but those stand out. Seeing as how I enjoyed Ghoulies and Conker:L&R, I'll check out their 360 games.