Here is a quick list of Power BI resources; blogs, training courses, documentation and videos.
Official Power BI Site
Microsoft’s Power BI site is at powerbi.com. Here you can sign up for the service, download the desktop tool, and get started with tutorials. The Power BI Official Blog is probably the best place to start and is updated almost daily. It’s here.
Microsoft Power BI Channel
The Microsoft Power BI channel on YouTube has a wealth of short videos on all aspects of Power BI here. It includes videos of the first Power BI conference, the Data Insights Summit held in March 2016.
Analysing And Visualising Data With Power BI
This is a fantastic grounding in Power BI essentials consisting of about 30 short videos. It is available as a playlist from the Power BI channel above and also as an EdX course here.
Guy In A Cube
The guy in a cube has short (under 5 minutes) weekly updates; a technical update on Tuesdays and a news round-up on Thursdays. His YouTube channel is here.
Reza Rad’s blog
Reza has a blog here. He is in the process of writing an online book on Power BI and chapters appear on his blog regularly.
Data Modelling And DAX
For good information about Microsoft tabular model and DAX
Marco Russo and Albero Ferrari have a DAX Patterns website. This is wonderfully organised. This answers instantly how to use DAX to solve your problem and then patiently explains the underlying principles underneath if you want to get the full picture.
See also their SQLBI website and their individual blogs
Chris Webb’s BI Blog
Chris Webb’s blog covers Analysis Services, MDX, PowerPivot, DAX and anything BI-related.
Dustin Ryan’s Blog
Dustin Ryan’s blog covers much of the Mycroft data Platform including Power BI and DAX.
Desert Isle SQL Blog
Ginger Grant’s blog covers many articles on R and SQL Server.
The Project Botticelli site covers Microsoft BI, MDX, DAX and data mining. Some articles are free but most are available at reasonable subscription rates.