Just Cause 2, just 'cause grappling people to moving vehicles (esp. jets) NEVER gets old

Terraria. The most addicting game for me since Dragon Age: Origins was released plus its early cheerfulness and easy-going nature lights me up.

Orcs Must Die! gets an honourable mention as well for the same reasons.

I love the following games, either due to cathartic violent actions, or humour...or both:

Day of the Tentacle
Grim Fandango
Full Throttle (never get sick of hitting Cave Fish)
System Shock 2
Plants vs Zombies
Godhand
and Good ole Deathmatching in Quake 3 Arena, or Unreal Tournament 2k4

Anachronox, for sure. The game's zany humour never ceases to surprise me. Just when I think I've seen everything, another ridiculous moment comes from behind the corner. :D

When I'm having a hard day I usually don't feel like gaming, but something like Quake Live gives a quick fix on needing to destroy something.

Monkey Island
Super Mario Bros 2
Zelda : Link To The Past
Portal 1 6 2
Chrono Trigger
Final Fantasy IX

Dead island for some reason

Curse of Monkey Island, because no matter how much life sucks, it can never be as bad as being a disembodied skull with fish nibbling on your feet at the bottom of the ocean.

Tales of Monkey Island!
The way Guybrush is a mighty pirate, but also a somewhat average person. He's always making a wisecrack or saying something funny. Wow, we recommend Monkey Island within 3 mins of each other. Great minds think alike!

Worms 2 or Amageddon.

Nothing cheers me up as some matches with these little cute worms :)
(Always using the polish speech bank, as it is the most funny language in the game)

a round of Ignition with someone on the same computer

I had a thread about this a while back, "feel good games."

Under a Killing Moon and King's Quest VI are big ones for me. Nostalgia overload is generally the best way to cheer me up. Same goes for 80's television.

Age of Empires 2. Used to get my ass kicked a lot in school and nothing was better than coming home, chilling out, and kicking some noobs ass on the multiplayer.

Grim Fandango
Darksiders 1 & 2
Simon the Sorceror
Giants Citizen Kabuto
Redneck Rampage

I like to play something with a bit of humor to cheer me up usually.