Dunno how people feel on talking about private servers, but I was looking to find a NA one with a good pop? Played on an EU one over the weekend but it was quite with people over there being asleep.
I recommend Turtle as well. The extra content is generally really good as well. Fits pretty well into the world and makes levelling a new character really fun.
What's also cool, for an NA player, is that Kalimdor and Eastern Kingdoms have different time zones. So you don't have to play in eternal night even though it's an EU server
Eastern Kingdoms has the normal server time, with the server being in the UK and Kalimdor is an 8 hours difference (+8 hours if I'm not misremembering)