For some people the barrier to pick up Power BI is learning the Power BI language DAX (Data Analysis eXpressions).
To hold down a very intense contract on Power BI (backed up with 3 Linkedin recommendations on http://www.linkedin.com/in/kieranpatrickwood) I created a Word document where I documented the most commonly used DAX commands that I used within this contract. So when I received a new business requirement which I needed to implement in DAX in the first instance I re-read and updated this Word document to gain an idea of which DAX function I should use. I also looked at other resources such as those listed within … http://www.innovativebusinessintelligence.com/Resources.
In the interests of serving the Power BI community and saving people from going through the pain I went through I have converted this Word document to a web page http://www.innovativebusinessintelligence.com/DAXReference .
Of course the above is a work in progress as my knowledge and experience of DAX grows. As always your constructive feedback is appreciated.