New Google Ocean and Google Mars
Previously, Google Earth imagery was very crude for the 2/3 of the Earth's surface that is covered by water. Now Google Earth includes global bathymetric data and labels for underwater features like seamounts, ridges, trenches, reefs, and geographic boundaries of marine areas. The underwater relief is clearly visible from a far off view of the planet's surface, but the really cool features start when you zoom in. Now the program allows users to dive beneath the ocean surface and explore the aquatic world below.
To get the full effect, I recommend first tilting your view at a near-horizontal angle so you can see the horizon before making the watery plunge. There are many layers available with ocean-related content such as dive/surf spots, ship wrecks, ocean expeditions, marine life tracking, and much more. If you're saavy enough to generate your own KML files, you'll also be happy to note that now the KML schema allows negative elevations, meaning objects can show up correctly underwater (good for me in my line of work dealing with underwater earthquakes). For more information, check out this Google Earth Blog post or the videos below.
I've blogged previously about using layers to turn the Earth into other planets in Google Earth. For the past couple of years, Google Mars has consisted of a Google Maps webpage showing Mars MOLA altimetry. As cool as that was, it didn't give you the full 3D Google Earth experience. Resourceful Google Earth geeks dutifully produced various Mars overlays and layers that can be used within Google Earth to make it seems like Mars. However, there are limitations to that approach, particularly with performance and with the lack of any 3D relief.
Now, in Google Earth 5.0 there is a full-fledged Mars mode. After launching the application, just click on the icon at the top of the screen with a ringed planet on it. If you leave your mouse hovering over the spot, it'll tell you that you can "Switch between Earth, Sky, and other planets." This implies that in the future, Google may add other planets such as the Moon too. Not only does Mars mode in Google Earth show actual imagery of Mars draped over 3D terrain, it displays more detail as you zoom in just like in Earth mode. The highest resolution imagery available comes from the HiRise camera, which is about 0.5 meters per pixel. That's about the same as the best images in Earth mode. Of course, there are labels and layers showing feature names, lander sites, rover tracks, etc. too. You can even interact with panoramic PanCam images taken by the Mars Exploration Rovers. For more information, check out this Google Earth Blog post or the video below.
The video below provides a general overview of Google Earth 5.0, including its other really useful new feature that allows you to go back in time and see decades of historical imagery.