If you have ever been curious about how an MMORPG is made or wanted to make one yourself then the resources below should provide a great starting point. 

A Beginner's Guide to Creating a MMORPG 
Excellent article that describes how to get started in making your very MMO games. Consists of 7 steps that include: assessing your skills, making a preliminary design, choosing and internal protocol for data transmission, the client, and security, getting a team, and dispelling myths about MMORPG development.

Eternal Lands' MMORPG Postmortem 
Read the thoughts of the founder and co-owner of the free MMORPG entitled Eternal Lands. This is a series of articles. 

Game Development Forum 
One of the best resources for discussing and learning about various aspects of online and non-online game development. 

Multiplayer Game Development Forum 
Game development forum dedicated to multiplayer games and networking. 

Massively Multiplayer Game Development 
"Massively Multiplayer (MMP) game development is one of the fastest growing areas in the game market...provides a "big picture" design process and includes valuable insights learned by the Toontown Online team, as well as practical online customer support issues learned by the Ultima Online team."

Developing Online Games: An Insider's Guide 
"A soup-to-nuts overview of just what it takes to successfully design, develop and manage an online game. Learn from the top two online game developers through the real-world successes and mistakes not known to others."