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.
However, the cases where installed base is relevant is a serious failure. Wave and Buzz come to mind.
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.