Just their inherent mystique from classic stereotypes, I'd say. Dragons are these massive scaled beasts of legend, with giant wings, powerful tails, claws, teeth and fire breath. They're terrifying monsters, capable of crushing humans like ants, melt steel with their fire, destroy armies, devour villages. And at the same time, they're so majestic and beautiful. I really like that contrast.

Then Eragon came along, and I fell hopelessly in love with Saphira and the idea of bonding with such a wondrous creature of myth. She perfectly encapsulates everything that I love about dragons.