GMail strikes me as a good example. Google maps. Can't think of any from Microsoft, but that's probably just because I haven't used a Microsoft product in 3 years. Actually Bing seems to be doing decently well.
I find it telling that for a big company, their major successes (as a big company) are typically software that do not need an installed base to add value. Mail and Maps are both applications that stand on their own and it is irrelevant what application your friends are using.
However, the cases where installed base is relevant is a serious failure. Wave and Buzz come to mind.
My understanding is that Google Maps was largely an acquisition: Where 2 Technologies, from Sydney, acquired in Oct. 2004. Its founders were, incidentally, the Rasmussen brothers, more recently known for Wave.
Maps in its present form is basically the fusion of an acquired startup (Where 2) and an internal project (Google Local, done by Bret Taylor and Jim Norris, later of FriendFeed and FaceBook fame).
As I understand it, the original Where 2 product was a desktop app, much like what became Google Earth, and not all that groundbreaking because satellite-imagery desktop mapping apps have been around since the mid-1990s. Google Local, meanwhile, was a search product, much like the current Local Universal search experience.
When Where2 was acquired, there was a flurry of interest in how to get that beautiful satellite imagery and user experience onto the Web, where the rest of Google's products were, and that's how Google Maps was born.
