We're doing a lot of training in Microsoft's Power BI, from PowerPivot in Excel to the new Power BI service.
To help our trainees, and anyone else that finds it useful, I've collated a number of resources we use to learn and teach Power BI, I hope you find them useful.
Applied Microsoft Power BI - bring your data to life
by Teo Lachev and Edward Price
Teo pulls of a difficult job in writing about a service that is updated monthly. This is a good primer to learn the basics for Power BI, but be careful that it may get out of date quickly.
Power Pivot and Power BI: the Excel users guide to DAX, Power Query, Power BI & Power Pivot in Excel 2010-2016
by Rob Collie and Avichal Singh
Rob has a really great writing style, clear and entertaining. He covers the basics of the "Power Tools" from the point of an Excel user, reccommended reading.
M is for (Data) Monkey
by Ken Puls and Miguel Escobar
On of the few books on "M" the languag behind Power Query and Get Data in Excel 2016 and Power BI. A great book to learn the powerful ways you get get and "mashup" data.
The Definitive guide to DAX: Business Intelligence with Microsoft Excel, SQL Server Analysis Services and Power BI
by Alberto Ferrari and Marco Russo
The title say it all really, "The Itallians" have produced the definitive guide to DAX. They start simple, but rapidly get into complex and powerful DAX programming.
Websites & Blogs
Microsoft Power BI Community - If you're serious about learning Power BI you should really join the community. Forums, examples, and advance information is all there.
Power BI Custom Visualisations - Pimp your dashboard with some custom graphs, charts and images.
Create a memory-efficient Data Model using Excel and the Power Pivot add-in - great page from Microsoft on making an efficient Data Model
Getting started with R scripts and R visuals in Power BI Desktop - Dip your toe into another new language! "R" lets you make custom visuals for Power BI Dashboards
PowerPivotPro - Rob Collies home website, packed with information, tips & tricks on Power Pivot and Power BI
Chris Webb's BI Blog - Microsoft Analysis Services, MDX, DAX, Power Pivot, Power Query and Power BI
There are many other Power BI resources out there on the internet, but these are the ones I find myself referring back to regularly. If you have any favourite sites I haven't found yet, feel free to pop details into a comment below.