War of Giants : Google, Yahoo, Microsoft & Apple
I found a nice chart @ theWindowsClub which illustrates many of the services these companies provide. 
Some of their products have been cornerstone revenue streams, and others are just at the beginning of development. But putting them up against each other really helps illustrate each company’s focus and their possible future directions of exploration. Seems like Microsoft has a very few remaining areas to try their hands on and conquer in.
