May 2014 Blog Task 1

Many of us have favourite websites that we return to over and over again. I can remember using VolkanoWorld,Bing maps when I discovered they had OS maps, Google Earth for the visual power to zoom in from a planet to a place bringing with it some idea of scale. So, our first blog task for May 2014. Please nominate one favourite website. How you use it and any tips for new users. Post these as comments below this post so that we can share a variety of ideas. Who will nominate first?