When learning something new, often available resources are lacking in some departments - whether they're missing information, poorly written, or tedious and dry. But occasionally, some content just stands out as above and beyond the rest, serving to not only make the learning process enjoyable but also to kindle interest in further exploration. What is that for you?

This could encompass everything from computer programming to literary criticism, and could be in the form of a website, book, video tutorial, or the like.