With CSS3 we can transform the appearance of elements by rotating, scaling, skewing or translating it. When adding transform css to an element it is applied before the page is rendered. Transformations can also be applied during transitions to create different animations. read more about using css3 transform

Since web 2.0 is the usage of gradients almost a must. Small background images were created for navigation menus, different sections or entire layouts. And when wanting to apply light changes like the height you needed to reconstruct the image(s). With CSS3 you can create gradient backgrounds and apply changes without much effort and it saves HTTP requests for images. Unfortunate do the layout engine not agree yet on the implementation of gradients. read more about css3 gradients

With adding shadow effects to text and a box you can eliminate photoshop to create this effect. The CSS shadow effects are more dynamic which makes it more easy to apply changes. The css3 text-shadow is a slightly moved, possible blurred copy of the text. It can be used to give some depth to text or to give it a  glow. Hopefully will this feature not be overused by some of the beginning  web designers.
read more about css3 text-shadow

One of the most wanted features in CSS3 is giving a shadow effect to an attribute. This effect was previously achieved by applying images to attributes using css2. You needed to created extra divs in case of box-shadow or a whole image if you want to apply shadow to text. This way of working was cumbersome and it was not always easy to apply slight changes without having to recreate the used images. read more about css3 box shadow