What was that movie that had people stranded on an island?

Were the people stranded on the island FBI trainees? If so, there was a movie called Mindhunters starring Christian Slater and Val Kilmer that fits your description.

"A group of seven FBI trainees is sent to an isolated island for the final stage of their training period under the direction of the eccentric Jake Harris (Val Kilmer), who uses questionable methods. However, they are attacked and killed by a serial killer that can be one of the team members. The tension increases amidst the group with the lack of confidence on each other."

Is it a newer film?

Try the perfect getaway with Milla Jovovich

or murder island with Marie Nilsson

I know exactly which movie you're talking about but I can't remember the name. Now it's going to drive me insane...

Here This is the trailor for that, I think your talking about this one http://www.youtube.com/watch?v=vC6um9Ubo_w