Hang works of art or art posters on the walls, colours, plants.....
Have a weekly dress code day.
Put up more of our photos around.
Play music in the office or radio FM, (all day, morning only or after 5pm.....)
Add flowers and plants to the workspace.
Have a weekly quiz of the week.
Have a toy section in the office.
Example: http://www.youtube.com/watch?v=4YhVyt4q5HI