What are some good resources / communities for CTOs, engineering managers, software development managers?
Wow...what a big question...here's a few answers...
The most important thing to know is that 90% of engineering management is culture management. If you build the right culture, then the engineers will manage themselves. So, do some web searches on engineering team culture and read those types of blog posts.
Also, read this: http://algeri-wong.com/yishan/engineering-management.html.
Additionally, you can read my blog, I've written quite a bit about engineering management (but I don't write as much as I used to): http://scottporad.com.
I follow Hacker News regularly. Personally, I spend my time on the "new" page instead of the "most popular".
I developed a deep understanding of Agile and Lean Startup methodologies. The key wasto understand them philosophically and strategically, as opposed to simply understanding them tactically. Once I understood them at their essential levels, the principles could be applied to all types of organizations.
Another thing I've done is to identify other organizations that served as "role models" for my team. Then, I would follow their blogs, find the slides from when they speak at conferences, etc. I would look for companies with similar technology, that appeared to be leaders in their space.
Of course, find yourself mentors with whom you can discuss your issues. Obviously, you can find those people here on Clarity.
Finally, in Seattle, where I live, we have a Seattle CTO mailing list consisting of senior engineering managers from across a broad set of companies. Find the version in your city, and if doesn't exist, start one.