Sapphires are one of the most popular jewelry stones that actually come in a variety of colors except for red, in which case would be a ruby. Sapphires, the September birthstone, weigh more than diamonds, so a sapphire and a diamond of the same carat size will visually look different.
Prince Charles gave Lady Diana a sapphire engagement ring, which is now famously worn by Kate Middleton.

Cut: Oval blue sapphire
Carat: 18 carat sapphire
Setting: Sapphire surrounded by 16 small diamonds in a cluster setting
Jeweler: Garrard Jewelers, London
About this ring: It was chosen from the regular Garrard catalog and therefore could be purchased by anyone, for the price of 28,000 British pounds, or the equivalent of $65,000 (at 1981 exchange rates).