Leonardo da Vinci is one of my favorite artists, though I appreciate and enjoy the expressiveness and delicacy of his drawings and studies far more than his paintings, which in all honesty I find rather ordinary (perhaps because that was the commercial/mainstream art of his time?). The piece below is a particular favorite (you may find the bird a few times in my sketchbooks), quite a departure from his 'regular' stuff yet just as ahead of its time as everything else.

da Vinci drawing

a small da Vinci web museum

The best and most complete (and therefore HUGE) book I've seen on da Vinci, his times and works is LEONARDO DA VINCI published by Reynal and Company

If you have come in the back door of Erik Johnson's Virtual Gallery via a net search, I suggest you try the front door...