Celestia is amazing for observing every star, and their known planets, including our own, in full 3D. Including other Galaxies. And the stars we know in them. Simply look at the sky click anywhere on screen, and you will click on a star, press space, and you zoom all the way to it's location passing by all the stars in between. Because unlike Google Universe, all the stars in Celestia are mapped in 3D and and are themselves in 3D. Like one giant Cosmic Space Simulator.
On the other hand Stellarium is an amazing observation tool, it shows you all the stars, planets, nebula, constellations, and more, visible from your geographic co-ordinates on Earth. Good for stargazing and using your telescope, to find where the planets you want to look at are, in real time. I like how it also simulates day, and then you cant see any stars, just where they are. I absolutely love it's clean minimalistic interface, it's a beautiful program.