So in a couple of days I am going to run my first play test for the game I am working on.

Setting: http://www.indie-rpgs.com/forum/index.php?topic=29551.0
Some System Info: http://www.indie-rpgs.com/forum/index.php?topic=29602.0

This test is primarily to try out the core rules, focusing on combat, and to see if what I have so far is fun to play.

I have 6 players, 4 from my regular group and 2 more that I game with off and on.

The outline is that they are on a high speed maglev train headed to New Jericho.  Because the train passes through large lawless areas it is heavily guarded.  However train operator is having a contract dispute with their normal security company so mercenaries have been hired to take their place.

Unfortunately for them the guards belong to the Daggers of Solomon, a terrorist organization that opposes Mobius and seeks to take control of the Tower of Babel so that "all may enter the Kingdom of Heaven".

They will take the train hostage and plan to blow it up when it reaches downtown New Jericho unless their demands are met, and there is no chance of that happening.  It is of course up to the players to stop them and save the train.

What I am looking for are some interesting situations/challenges to throw at the group so it is not just a series of similar combats.  Two that I have come up with are disarming the bomb(s?) and Hacking into or bypassing the trains security system.  Besides that you have the fairly obvious enemies hiding behind hostages. 

Any suggestions what else I could throw at them that would make the experience memorable and unique? 

I would suggest watching some videos of Uncharted 2's train sequence.

A battle on top of the train or on an open car. Some reason to hang on the side of the train. Some sort of helicopter equivalent attacking them from the sky and forcing them to retrieve some of the terrorists weapons to take out. Some sort of heavy weapon in a car that they have to attack by the aforementioned climbing around outside.

Sounds fun, I'll look into those.