Seems like a mundane answer, but Wikipedia is an outstanding source without a finnish line. I have created for myself several "Wikipedia books" that consist of aggregated Wikipedia articles on specific quantitative subjects. The results are self-customized world class textbooks-equivalent on any statistical or quantitative domain of your choosing. And, whenever you are intested in a new methodology you can add it to your Wikipedia book and it essentially creates a new chapter for it, including the article. Just learn how to create those Wikipedia pdf files that you turn into a book and you are set.
The above, I think, is a highly underutilized capability of Wikipedia. Although it is really easy to do, I don't know of anyone else that has used this method to boost their learning by creating easily worldclass reference material.