Google Earth is the last marvellous thing you've to discover !
Better in resolution than World Wind, it adds the usefull meta-information on top on geographically located places ! And imagine the diverse application it can have. Google with it tons of links in its search engine database can inform you on quite anything.
Find a city, building, a shop, a webcam, routes, railways, airports, hotels... "The idea is simple. It's a globe that sits inside your PC. You point and zoom to anyplace on the planet that you want to explore. Satellite images and local facts zoom into view. Tap into Google search to show local points of interest and facts. Zoom to a specific address to check out an apartment or hotel. View driving directions and even fly along your route. We invite you to try it now."
Perfect satellite image quality: Keyhole
30cm resolution in many big cities (US, Paris...)
The program lets you do smooth sailing flybyes of the entire Earth. You can easily fly to any spot on the globe, by entering any associated data, like street addresses, place names or lat/long coordinates. There are overlays that put additional information on the map, like roads, international boundaries, terrain, 3D buildings, crime statistics, schools, stadiums, any number of interesting stuff.
You can do Local searches in the program, with icons on the map and a display on the side showing your results. You can leave notes, called "placemarks" all over the map, so you can remember where all sorts of places are. Searches and placemarks can be saved as bookmarks in "My Places". Everything can be output in an XML format called KML, that will allow the vast popularity of Google Maps to continue in Earth. You can also email a JPEG of the map, or send a KMZ file if you know the recipient has Earth installed.
Google Earth Plus gives higher resolution images, GPS support, and more sophisticated annotation (like drawing on the map). Online help is available
right here.