Want to know pretty much everything about a website - just take a look at QuarkBase. This is one of the few sites that really blew me away.
QuarkBase gives you an incredible overview of a websites information. Everything from Delicious bookmarks to People Information and site software is included.
Sure there are plenty of sites that will give you this information (probably not all at once), but QuarkBase executes this task in a streamlined and intelligent manner. Features like detecting the sites a blog and which software its using is nifty - and bring together info from CrunchBase is also a smart move.
I don't know how QuarkBase plans on making any money - but I do hope this incredible service sticks around.
10/10 Well Done QuarkBase!