The first resource I’d consider is the Cordova blog. Not technically a separate site from the main home page, the News link acts like a blog and is a handy way to get notified about recent changes. There is an RSS feed (http://cordova.apache.org/rss.xml) you could add to your favorite reader or consider using an IFTT RSS to Email recipe (like I am adding myself right now!).
On the PhoneGap side, check their blog as well. By default, they aggregate posts from the community as well as write their own content. So if you already follow folks in the community and want to focus on “official” PhoneGap news, view just the PhoneGap news here: http://phonegap.com/blog/phonegap and Build news here: http://phonegap.com/blog/phonegap-build.
While folks may debate the relative value of Twitter (I go back and forth between full on addiction and disgust), you can follow official accounts here: @phonegap, @apachecordova, and @phonegapbuild. There are – of course – various team members who use Twitter regularly but I’m not going to list them out by name. (Because I’m lazy. And I’m hoping someone has built an official list already!)
Another option is the Cordova developer mailing list. To be clear, this is not a support list. Rather, this is where the developers of Cordova discuss things. It is a pretty busy list. I’m subscribed, but generally focus on items that look important. So I’m less concerned about the discussion of API X but rather the end result so that I can help others with it in the future. But if you want to be in the know about changes even before they get released, this is where you want to be.
That covers keeping up with the projects, and I hope this is helpful. While not directly related to the subject matter at hand, I want to point out the directory of PhoneGap Meetup groups. Thank you, Holly for reminding me of this. Also remember that you can find PhoneGap developers at the PhoneGap developer directory.