After Greg rained info on me like mana from heaven, I've taken it as a personal challenge to respond in kind. Here we go, +Greg Bayles. Have some stuff on digital civilizations/nations and virtual worlds.
This article is a chapter from this book that deals more with privacy, but also suggests that Facebook deserves a constitution, especially since David Cameron (Prime Minister of the UK) met with Mark Zuckerberg as if he were a head of state.
This is a reddit user's attempt to make a whole constitution for the "Digital Nation."
This image is from Gary's Mod which I found from this reddit thread where a lot of users talk about how they've "lived" inside the game. In addition to going to a bar to watch professional gamers play another game from inside the game, people have read the entire Lord of the Rings series, watched whole movies, and more.
This article is about the upcoming EverQuest Next, a game which is actually two games presented in two phases. The first phase is EverQuest Next Landmark, where players will be free to establish towns, settlements, cities, etc. to establish the world, then when that phase is done and enough of the world is built, they'll start the real MMORPG of fighting and stuff, but you can still build things too.
I haven't seen Greg talk much about Second Life, so here's a book (check out the Amazon suggestions at the bottom for even more--even a guide on building a business in Second Life), an article about some ethical questions it raises, and a video showing how one woman used Second Life to relieve the symptoms of Parkinson's and create a "reality in a different form" for herself. (Posting that video on Google+ got almost an instant response from its creator +Draxtor Despres, whose posts offer endless interesting material about second life as a virtual world.)
Small Worlds is a more cartoony, more social media-centric virtual world, and this article shows a few others like it.
An idea that seems to be HUGE that I had never heard of before is the Metaverse. From what I can gather, this is a large-scale collaborative effort to guide a single, cohesive virtual world alongside the real world. Get what you can out this website here, but make sure you check out their "Metaverse Roadmap" here.
Uniiverse is a digital service to help people meet each other and find events they would be interested in in real life.
The Odin Project is a group trying to build a virtual world that's based here at BYU. I honestly don't know very much about this group, but they may be able to help you if you get in contact with them. For more info, you can contact +Martin Mumford at email@example.com.
Okay, I'm running out of time to work on this post, and it turns out that I may not have found quite as much as Greg did, but I hope this helps.
Good luck, Greg!