This is a collection of Resources related to Umbraco which I believe will be useful to those who are new the the CMS. I plan to keep this updated. If any of these links break, or you have any suggestions for additional resources, please let me know.

An Agency’s Guide to the Umbraco CMS — In this book I share the best-practices I have gathered from over 20 years of experience in a concise format to give you a quick start with no fluff.
Free E-Course: 5 Ways to Save Time When Building an Umbraco Website — Written especially for agencies new to Umbraco development, this 5-part e-course will share tips on project-management and development to get your Umbraco projects off to a good start. — Support forums, package downloads, videos, official documentation, releases, etc.
Skrift MagazineA monthly magazine for sharing knowledge in the Umbraco community
24 Days Umbraco Advent Calendar — Annual "advent calendar" of community-supplied articles counting down the days in December
Umbraco.TV — Training and how-to videos created by Umbraco HQ Videos — Videos including Codegarden session recordings 2015-2018
Umbraco HQ Vimeo ChannelVideos including Codegarden session recordings 2010-2016
Umbraco HQ YouTube ChannelVideos including Codegarden session recordings 2019
umbraCoffee — Each week, on Friday 12:30 CET, Marcin and Callum from The Cogworks - together with their guest(s) will drive you through the weekly news and things Umbraco related.
Codegarden Conference — The annual HQ-sponsored event held in Denmark.
Umbraco Festivals — Umbraco conferences ("Festivals") happen around the world annually.
Meetups — Umbraco Meetups are happening regularly all around the world.
Twitter — There is an active #Umbraco presence on Twitter.
Umbracians Slack Group — Free-form conversations and community announcements.
Umbraco Gitter — Another free-form chatting platform. Not currently very active. 
UPractitioners — A virtual meetup for anyone involved in Umbraco projects: Strategy, UX/UI Design, Marketing, Content, Project Management & Front-end/Back-end Developers.
The Bob & Kevin Show — Podcast from long-time Umbraco community members Bob Baty-Barr and Kevin Giszewski talking about a lot on non-Umbraco tech topics, but frequently chat with with other Umbraco community folks.
GitHub — Repositories for Umbraco CMS Core, Documentation (yes, you can contribute to that as well!) and other things.