The best way to improve the teamwork quotient in your team is through training games. If you have a fulltime trainer on the rolls of your company, you will know that they use a large number of training games in their sessions to get the team energized.
Actually, you donot need to be a trainer to make use of training games in your work. Anyone with a bent of mind to get his team to perform well will find training games useful. The most popular games are those which have the least amount of resources. So it does not even take you a lot of preparation and cost to get the game going. Some of the most powerful games could include just a few newspapers and a few paper clips! Some other games donot even require those. Then there are games which require a lot of preparation and groundwork; and those are effective too.
If you are looking to boost the team spirit in your office, the best way would be to get them to participate in training games. If you donot want to do it within your office, think of an outbound training program where everyone goes out of the office and heads over to a place where it is kind of like a picnic, and they also play a few training games. Either way, the teamwork factor will receive a big fillip.