MMORPG Netcode library

Perhaps Nevrax. But in the end I would suggest the best place to look is in your mind. Anything you find will have to be manipulated to fit your needs and will never be 100% of what you want if you had written it yourself.

i prefer RakNet.

For future reference the link is http://new.nevrax.org/tiki-index.php

The networking forum is the right place for this question. It also has a Forum FAQ you might want to look at, as it has a good list of networking libraries.