I think the subject explains itself. Already have Super Mario 64.

Legend of Zelda Ocarina of Time and Majora's Mask
Starfox 64
Super Smash Brothers
Mario Cart
Golden Eye
Perfect Dark

Given your avatar, I'm guessing that Ocarina of Time and Majora's Mask are also a given. Let's see...well, you might want to check out Banjo-Kazooie, Star Fox, Golden Eye and Conker's Bad Fur Day.

Let's get the bigger ones out of the way
Ocarina of Time
Majora's Mask
Pokemon Stadium 2
Pokemon Snap
Mario Kart

My personal favorites:
California Speed
Super Smash Bros

Donkey Kong 64. It's still my favorite 3D platformer.

Wave race 64. One of my favourite games.

Mario 64
Donkey kong 64
Kirby 64
Golden eye 007
Perfect dark ( only if you have the expansion pack for your N64)
Turock 1-3
Star fox 64
Pokemon stadium ( only if you have pokemon red/blue)
Zelda OOT/MM
Bomberman 64

Banjo Kazooie 1 and 2.

Wipeout 64 :D

Most wipeout games are the tits.

Better than F-zero... just.

Theflyingass:
Banjo Kazooie 1 and 2.

Definatly this. Also add Conkers Bad Furday to the list. Basicly get anything Rare did on the N64, its all good.

Johny64:
I think the subject explains itself. Already have Super Mario 64.

One game is a must, Conkers Bad Fur Day because it has Nazi teddy bears, terminator-esque stacks of hay, hillbilly pitch-fork, flowers with breast, ferret mafia guys, t-rex riding, lava surfing, giant opera singing poop, Dracula squirrels, death with an English accent, a German robot scientist, matrix scenes, scenes from the movie Alien and a alcoholic swearing squirrel as the protagonist.

Road rash 64. Great game and if you can get some friends to play it with you, you´ll have tons of mad fun.

Since I am sure everyone is just busy recommending super well known titles. Here is an obscure one for you. Body Harvest.

ocarina of time
majoras mask
mario 64
golden eye

I agree with what has already been said, so all I can suggest is something less popular.

Space Station Silicon Valley.

Banjo Kazooie
Banjo Twoie
Donkey Kong 64
Mario 64
Lylat Wars [Star Fox]
007: Golden Eye

And anything Rare did.

Pretty much what everyone else has said.

Plus Body Harvest. It's sort of a sci-fi precursor to Grand Theft Auto (made by Rockstar before they become Rockstar). What a great underrated game that was.

And Doom64 - it managed to successfully mix the Doom run and gun formula with genuine psychological horror (it has a terrifying atmosphere). It's what Doom 3 should have been.

Rogue Squadron
Pokemon Snap
Majora's Mask
Blast Corps
Jet Force Gemini
Extreme G

ON another note I would certainly buy 3DS ports of all of those too.

Heres a few games that I think anyone with an N64 should play;

Quest 64
Starfox 64
Legend of Zelda: Ocarina of Time
007 Goldeneye
Perfect Dark
Super Mario 64
Kirby 64

Hope this helps ^_^

Palademon:
I agree with what has already been said, so all I can suggest is something less popular.

Space Station Silicon Valley.

I thought I was the only one who remembered that game, I second this suggestion.

Mischief Makers
Body Harvest
Turok 1 and 2
Buck Bumble
Most things from nintendo

Glover!
get glover!!!
harvest moon 64 is also good

Donkey Kong 64.

If you like Mario 64, you'll probably enjoy DK.

I think it may be the game Rare has made.

Kirby 64! you'll beat it in 3 hours but you will play it over 100 times.

Hmm weird clock must be wrong, says it 2012, but that can't be right.

Well anyways while I'm here (or now?) I would recommend Goldeneye, both zeldas, and super smash bros, especially if you can get a couple mates together.

A topic that isn't about wRPGs for once. My savior.

Definitely play Paper Mario.

I cannot recommend this enough.

Paper Mario. Just like LilithSlave said. My bro just finished playing the game like yesterday.

Conker's Bad Fur Day is another.

And the original Super Smash Bros. But only if you have a few friends and controllers.

Turok: Dinosaur Hunter and Turok 2: Seeds of Evil. The other two (actually all the other Turok games in general, really) are pretty shit.
Perfect Dark has aged surprisingly well if you can get used to the controls, but you'll need an expansion pack, or you'll be limited to botmatches.
Body Harvest, on the other hand, has not aged well, but if you can get into it, it'll get into you.
I'm even shocked that I'm saying this, but Superman 64 is passable if you get really, really stoned (seriously, you'll need a hookah packed with the stuff that makes you drool on yourself) and all you do is fly around the city, and do nothing else. Oddly serene.

Everyone else has already mentioned everything else I know of.

The Mario Party games were fun. I also suggest Gex: Undercover Gecko and the Banjo Kazooie games, as well as Super Smash which has been suggested a bunch, as I should be. ^_^