Chip Pearson is a professional developer with a long history with Excel. His site, www.cpearson.com contains a huge and diverse repository of useful Excel information. In addition to a detailed topic index (over 300 entries), you can find a dedicated downloads page and a what's new page. Many of Chip's articles are extremely comprehensive. For example, see a Description of Array Formulas, and Ranking Data In Lists.
Note: Chip passed away due to an accident in 2018. He was a titan in the Excel community and will be dearly missed. His site remains online.