IPleak.net looks to be a pretty comprehensive website that allows you to check what IP address websites you visit see you as coming from as well as various other bits of info your computer might be leaking to advertisers and other dodgy operators. Your IP address can be used to establish various bits of info about you such as who your ISP is or whereabouts in the world you are for example.

The site also shows you what can be established from the DNS servers you’re using, what information is available to others from your web browser and even has a clever way to see what IP address any torrents you might prospectively be considering downloaded will see to via adding a “fake” magnet link to your Torrent client.