Activities - Plan group activities where everyone gets a chance to participate such as bowling or paintballing.
Group Lunch - Organize a team lunch outside of work where everyone sits together and has a chance to interact outside of the workplace.
Retreats - Team retreats can do wonders for team building, especially if you go to a retreat that has a team building curriculum already in place.
Games & Ice Breakers - Games and ice breakers are a fun way for a new team to get to know each other and a good way for a new team member to get to know everyone else. It can also be good for acquainted team members to learn more about one another and to just have fun.
Outings - Social outings where team members have a chance to interact in a stress-free enviornment gives the team members to socialize about non-work related topics and builds up their relationships on a personal level. Barbeques, a day at the beach and picnics are just a few ideas for outings.
Sports - Sports are a great way for teams to bond, but be sure to try to involve everyone, not just the best players.