The promise of web services is really starting to kick-off. Years ago when Amazon and eBay started offering APIs there was little sense that we'd be able to recompile the Web as imaginatively as we now seem to be able with the emergence of developer hooks from Google, Flickr et al.
Thanks to my good friend - Danny - who pointed out the awesome Housingmaps, which takes the best of Google Maps and adds in Craiglists to offer a real estate guide that would shame most others online. And then there is the beautiful Flickr Related Tag Browser, which Andrew discovered. We're at the tipping point here... keep watching.