Not a natural resource per-se, but Singapore's geographic location is very special wrt global trade and strategy, being at the tip of the Malaysian peninsula and in the Straight of Malacca. It's been a port and a nexus as a result for hundreds of years, a huge part of the equation of Singapore's success story.

edit: wikipedia says 25% of the world's trade flows through the Straight of Malacca - it's a big deal!