The Bellagio, despite how expensive a lot of it is, is home to two of the best free attractions in Vegas (fountains). Real flowers, real trees, and 100% free. Whether it's butterflies in the fall or polar bears made of carnations in the winter, the Bellagio really puts together some beautiful scenes.
It can get crazy crowded here, of course, but if you go late at night or early in the morning, you can be here when there are very few people as well.