Below are some of the sites/ blogs that I find interesting

SQL

• SQL Server Central
• SQL blog.com
• MSSQL Tiger Team

Power BI

• Guy in a cube (youtube channel)
• Avi Singh: the Power BI Evangelist
• Radacad
• Powerpivot(pro)
• Power BI Tips and Tricks

R

• R-bloggers

Visualisation

• perceptualedge (Stephen few)