https://www.ptable.com 
In the past, from time to time I have thought to myself, I need to take a look at the periodic table. I never studied it in school but I just had to find out about it, it fascinates me and sometimes i have looked at it for hours without getting bored. This dynamic periodic table is by far the best. You can click on any element for a detailed description of it, move the slider and see the melting/freezing/boiling points of all the naturally occurring elements and click on the other tabs for even more info.