Best (most realistic) physics game? Inspired by a similar post, I wanted to know what video games, past or present, most accurately employ the laws of physics. 
I believe this is an appropriate question for this site, since the users are far more qualified to answer it than anyone on typical gaming sites, who think they know a lot more about physics than they really do. In my limited experience, most games claiming "realistic physics" are anything but.
 A: POOL
A lot of pool(/snooker/billiards) video games are pretty realistic. 
Because implementation of physics engines of such games is relatively easy task. 
Here is one example. 
Other games in which some physics is real are


*

*Pocket Tanks
A: Mafia II (2010) currently has the world's best physics model for gravity, acceleration, driving and destruction of parts of cars (exact models of physical characteristics of dozens of types of historical cars), buildings, piling up of debris, ashes, broken glass on the floor, people, friction, fire, smoke, optics including complicated absorption and reflection models off different types of metals on the cars' surface, and everything else. 
In all those respects, it was a huge winner, as expected from a similarly groundbreaking Mafia (I) in 2002. 
However, the play fun itself is limited as people often think that there are not too many things to nontrivially interact with in the city and the tasks form a completely linear sequence which is often considered boring - even though this was the Mafia II's plan from the beginning because this leads to much more organized, movie-like experience. Mafia II - and dozens of other games that exist today - uses NVIDIA's PhysX enhancement of the physics calculations by graphics cards, see e.g. 

http://youtube.com/watch?v=GMHeIGjLZ9I 

If you want a more impressive, financially unrealistic but physically valid scene with thousands of barrels that are falling and exploding, see Crysis Physics

http://www.youtube.com/watch?v=YG5qDeWHNmk

which still remains a benchmark.
A: I was never able to do rigorous quantitative analysis, but in my memory, Scorched Earth always seemed very realistic, including proper trajectories, air resistance, and wind.
A: The original Asteroids arcade game has a very good model of rocket propelled flight in vacuum micro-gravity (Well, it neglects the matter of the fuel mass-fraction. So assume an unreasonable efficient propulsion system...). Of course, the space metric is toroidal and the collisions model is rather primitive... Edit: Wikipedia tells me that the ship in Asteroids would coast to a halt. I don't recall that, but it seems to kill this assertion. ::sigh::
Likewise the Lunar Lander game many of us recall from the 8-bit era handled vacuum maneuvering in a non-trivial gravitational environment. Again the collisions model was a bit simpleminded...
A: James McNeill is building an almost-true-physics lunar lander clone (with full rigid body motion, like compressing shock absorbers for example). The game is still work in progress but playable (see here).
Very interesting blog here.
A: I'm going to have to throw out a vote for X-Plane, approved by the FAA for flight simulation.
A: Quantum Soccer:
http://gregegan.customer.netspace.net.au/BORDER/Soccer/Soccer.html
Orbiter:
http://orbit.medphys.ucl.ac.uk/
Plasma Pong:
http://www.youtube.com/watch?v=NDjseVmruH8
A: Most first-person shooter today actually have a decent gravity model. Angry Birds is fairly realistic, for a phone game as well. 
A: Half-Life 2 has what appears to be nice physics, which are also involved in puzzles, where you, for example, have to move floating barrels under a broken bridge so it rises and supports your vehicle.
A: Real-life is pretty good (at most scales - it gets pretty unrealistic in the very small details)

A: Angry Birds.
It's a very nice game with realistic collision physics simulation. 
A: You should definitely look into Algodoo (formerly Phun) at http://www.algodoo.com/
This is not a game per se, just a "physics sandbox" - a game with no goal other than one you set yourself. Rich mechanics, fluid dynamics, air friction, motors, ability to change object mass, friction, flexibility, collision layers and so on...
Another game you might be interested in is the Powder Game, http://dan-ball.jp/en/javagame/dust/ much more simple but with rich particle physics simulation - various materials of specific properties: water(freezable, evaporable), explosives, magma, sand, rock, oil (burnable) and so on.
A: Have a look at 
http://gamelab.mit.edu/games/a-slower-speed-of-light/

A Slower Speed of Light is a first-person game prototype in which
  players navigate a 3D space while picking up orbs that reduce the
  speed of light in increments. Custom-built, open-source relativistic
  graphics code allows the speed of light in the game to approach the
  player's own maximum walking speed. Visual effects of special
  relativity gradually become apparent to the player, increasing the
  challenge of gameplay.

A: This post has been dead for a while, but I can think of a few really good PC games.
"Red Faction: Guerrilla" is the best example. 
Literally every object is destructible. On a dev showcase video they even say "we needed to stop making buildings that looked nice, and start designing buildings like architects, because the nice looking buildings would simply crumble under their own weight."
"Dirt 2" A racing simulator has awesome physics attached. Great car deformation.
A very un-known game "Cortex Command" is really good about physics. Every bullet / weapon / vehicle is made out of physical material, which can be destroyed.
If your PC can handle it, Crysis 1 has a relatively open world fully destructible environment as well.
As suggested above "Algoodoo" is a great physics sandbox. As is "The powder toy"
"GTA 4"'s engine is pretty good. Poorly optimized for PC, but allows for good vehicle deformation ect.
Some good flash games include "Fantastic contraption" and "incredibots"
