Here are a few various useful resources:
Microsoft Docs – Documentation on all things Microsoft, should contain almost all the articles from the old MSDN TechNet as well.
Stack Exchange – The root site for various excelent resources like Stack Overflow and Server Fault.
RegExr – Excellent site for creating and testing Regular Expressions (RegEx) strings.
SS64 – References for common scripting languages (across OS-es) and reference for database commands.