This game validates my purchase of a PSP. It's also is one of the few games to put me in a trance where I actually lose track of time.
2. Katamari Damacy
Nothing like rolling over a bunch of mindless people to take your thoughts off the mindless idiots you work with/for.
Hordes of undead + stakegun = melting the stress away.
4. Dead Rising
See above, but replace stakegun with anything else you can think of that isn't a gun.
Yes, it's new, but I'll be damned if it doesn't take me back (via Delorean style time travel) to the days of my N64 and LoZ: The Ocarina of Time. I mean, it's practically the same damn game... not that it's a bad thing.