Zombieland, without doubt.
It's not too serious, but it's just great to chill on the couch with a few friends, get a few beers and just enjoy the heck of it.

I love the various jokes (like the rules explained in the beginning of the movie, the "Zombie-kill of the week", etcetera), and it doesn't try too hard to be funny - it's just well executed and pure entertaining.
By the way, did anyone notice that every time Tallahassee was looking for twinkies, they were right there - hidden on the screen - but just out of sight for the characters?

Also, while it's not a real movie, The Walking Dead was great apart from the series' final episode. But the original had the same problem, so I don't blame 'em.