The 15cm Aluminum Ruler from Midori is a cult favourite and another winner of the Good Design Awards (2013) - this 15 cm ruler is made from a lightweight yet strong aluminum. It is laser engraved so that the numbers do not disappear over time and use.
With an aluminum edge, it can be used with a knife cutter. The slanted shape makes it easy to pick up and hold.
Also available in an aluminum / wood version.