Buzzwords
Buzzwords is a game that can be played throughout the evening and doesn't take a lot of thought. It's also a positive game because you can participate or choose not to play without ever saying a word. As the guests arrive, give them a clothespin, a pin on button, or a string of colored beads. As you do this, tell them the "buzzword" for the night. Choose a buzzword that they will be tempted to say often, such as "work," or "report," but don't necessarily need to say to have a conversation. Explain the game to the group after all of the guests have arrived. Tell them to avoid saying the buzzword. If someone hears them say the buzzword, that person can take their clothespin, button, or necklace. At the end of the night, the person with the most clothespins, buttons, necklaces wins.
Office Family Feud
Office Family Feud is a fun game to play with a larger group. The week before the party, send out a survey asking different questions, such as "Name a fruit," or "Most vicious animal." Count the answers, and make a list of the top 8 most common answers. Separate the guests that want to play into teams of 5 to 10, and play multiple rounds if more people want to play. Have each team try to name the most common answer for "Name of fruit," and rank their answer on the board, giving points for the top answers.
Pictionary
Pictionary is another game that any number of people can play. Set up dry erase boards around the room, and separate interested players into groups. Use the standard "Pictionary" board game for drawing ideas, or you can create you own ideas. Have a member from each team draw a picture, while the other members of the team guess in an allotted amount of time. The team that guesses the most will win.