R for Data Science is an incredible introductory text regardless of discipline (free here!). Mastering the tools in the book will give you the tools to approach most analytic problems.
Using R for Introductory Econometrics is a companion book to Wooldridge's introductory econometrics book. It doesn't rely on the tidyverse, so it may be a confusing sequel to R4DS, but it is a useful reference for econometric techniques.
CRAN task views are an essential resource for domain-specific R. The CRAN task view for econometrics is thorough.
I work at the Urban Institute. We have our own website for reference and sharing code called R Programming at the Urban Institute. It doesn't contain a lot of information about modeling, but it's useful for our research assistants. We're adding more content all of the time! We'll probably add some modeling information in the future. Requests and pull requests welcome!
Finally, the R community is amazing. #rstats on twitter is a useful resource! So are local user groups!
Thanks for doing this! I look forward to hearing suggestions from others!