Sapphire engagement rings? Absolutely! Diamonds may be a girl's best friend, but Sapphire engagement rings are a unique, original, and a far more affordable choice. Sapphire is the birthstone of September, and one of the most popular gemstones on the jewelry scene today. The deep blue color of a sapphire ring is just right for an evening out. The birthstone of December, the intense deep blue color of a london blue topaz ring can evoke thoughts of warm Caribbean nights.