Also wanted to add Tony Hawk's Pro Skater 3. Not only was it just really fun, but it didn't take itself too seriously. The skater choices were ridiculous too, which I loved. Pretty much the entire early Tony Hawk series was great.

This game is still just pure joy to pick up and play, and have a few laughs from the animations. Mario's quick feet get me every time.

Brawl Brothers is repetitive, but nostalgia makes it fun for a little while

Banjo-Kazooie comes to mind before anything else. Excellent level design, soundtrack, gameplay and most notably: humour.

Always brings pure joy to play it. (But I guess that can be said about pretty much any classic Rare title.)

Mario tennis
Donkey kong land
F zero
Zelda
Wii sports/resort

I miss quality Rare so much. Not that their current games are bad, but it's kind of sad when you look back on games like Banjo Kazooie, Perfect Dark, and Conker's Bad Fur Day (or pretty much any of their early titles for that matter).

Also listened to the Banjo Kazooie theme song just now and nostalgia'd hard.

Mega Man 3

Mega Man X

Kirby Superstar

All 2d Mario platfomers

DKC series (SNES)

Jet Force Gemini

Super Metroid

Legend of Zelda Link to the past.

I can play all the above games over and over again and never grow tired of them. To me they're pure fun.

Street fighter
KOF
PES
old school Sonic
Dbz budokai
Dbz tenkaichi

Red Faction: Guerrilla
Wii Play
50 Cent: Blood on the Sand
Happy Action Theater

You've made me want to dig out SSX 3 again now.  What an incredible game.

Well:
- Rat on... (Activity) games on iOS. They are always fun and addicting in short bursts.
- Mario Kart: Double Dash. Everyone hated it but it's the most crazy and fun game I've ever played.
- Spongebob game from GC: I'm too lazy to type the name, but the gameplay was fantastic and fun for hours.