URLInfo is a nifty utility built on Google App Engine that shows the hidden web server details of any site you wish to see. It is true that the data is good for nothing but if you see some sites you may find some interesting details.
As dailygyan notes webworkerdaily headers contain a job notification saying “X-hacker If you’re reading this, you should visit automattic.com/jobs and apply to join the fun, mention this…”, how cool it is. It gives some details about the platform the site is running, web analytics a site is using, no of images on the page and external and internal links. It also shows size of the webpage and load time. Checkout mine here