Flowers are the butterflies of the plant world. They're beautiful on their own. Good lighting or an interesting angle are just bonuses. I'm a fan of backlit flower pictures where some component of the flower has as a bit of a halo.
Lilly flowers make particularly good subjects. They're big and very vibrant looking. Their proximity to water means that there's a chance there'll be water droplets on the petals which is a nice effect. And they're not as likely to sway in the wind because they're sitting on water and attached to the ground by a pretty sturdy stem.