Capture the Flag
Terrorist and Anti-terrorist (also known as "set the charge/bomb")
Death Match
Take and Hold (multiple locations count as points, time limit game, which ever team has the most at the end of the time limit wins)
Break Through (One team starts at point A, needs to get to point B without being wiped out. Sometimes this has to be a set path, such as a road or set route)
Egg hunt (Objectives are hidden around the play field representing objects of importance, like spy data, secret documents, gold/platinum, etc. For each item found and turned in to a ref. or taken back to their teams base, or some other place set up before the game gets a certain number of victory points, which could tip the game in the favor of one team or another)
V.I.P. (Obviously someone IS the objective. He dies, the team defending loses points, the team killing gets points. This can be mitigated by the defending team by "Executing" their V.I.P. which will make them lose less points than if the opposing team had killed the V.I.P. The V.I.P. game could also be a rescue, or even an assault to extract)
This is hardly a comprehensive list, and really the best games are those that combine 2 or MORE of these in one scenario. For example, a Take and Hold mission (with a long time limit, 6 hours) with a VIP (or two), and an Egg Hunt (with items speratically replaced on the field at random locations, or middle of dead locked firefights to bring people out of cover) is what my last large scale game was.
The mission was set up so that one team was away from the take and hold area with a VIP. The other held all the Take and Hold positions. "eggs" where everywhere, hidden and once found returned to the field by the refs. There was another VIP in the take and hold area, but if he died, then BOTH teams lost points. The second VIP acted as a mobile Take and hold objective. The game was won by the Original VIP team by killing the first VIP themselves to keep points away from opposing team and to free up men to assault the take and hold area (without the other team knowing that the VIP was dead), then getting the most eggs and rescuing and extracting the mobile VIP. The Team that started in the Take and Hold area had control of ALMOST all take and hold objectives (there were about 6), but still lost due to the amound of Eggs found by the VIP team, lack of points for killing the first VIP and losing the Mobile VIP. This Of course that was with ~40 people (~20 per side). But it's a good example of how to mix objectives.
Anyway, that's all I can think of at the moment. As always, I'll post more if I can think of more.