The National Center for Men was mentioned in the below Michael Newdow article. Newdow says that the organization helps men who were tricked into being fathers, as he was. There isn't much there at the moment, so it might not be worth the click.
Now, I will acknowledge that women can be very manipulative but... uh... dude... did you miss Sex Ed in high school? Did you ever see the Discovery Channel? A sort of natural by-product of sex is a baby. If you didn't want that to happen, then maybe you should have kept your fly zipped.
This is not a comment about how unfair the legal system is in child custody matters however. There are many fathers who have had their children stripped from them and forced to fork over most of their income due to legal bias in favor of women. Wendy McElroy has written quite a bit on this topic (http://www.ifeminists.com for more).