Ok this movie is about people who live on a huge spaceship because something is wrong with earth or something. But every month or so there is a "random" drawing where some person gets to go to a tropical island. This guy investigates and finds out these people are dying or something like that.

It vaguely sounds like
Your describing

The Island

A group of clones is kept isolated and ignorant
Of the outside world in a remote facility/colony.

When an important person needs an organ they
Harvest their clone. The clone is told theye won a
Contest to live on a trpoical island paradise

One curious clone gets suspicious and investigates
The lottry system. He finds the winners are being
Dissected for their organs. He goes on the run with
His girlfriend

-view trailer- (http://www.youtube.com/watch?v=CnievsTG3x4&feature=related)

That's exactly it.