I have scoured the internet for a good twin site too, and I've had a pretty hard time finding a decent one, especially with a forum. I'd love to know if someone knows of one!
The Multiples forum here is pretty good, and I've gotten a ton of good advice, along with being able to share this pregnancy with other women who are pregnant with twins right now, and some moms who are pregnant with their second set, and even twin moms who are good at giving advice (Adorkable!).
Here's the link to that forum.
http://www.mothering.com/community/f/158/parenting-multiples
and the current "pregnant with twins" thread:
http://www.mothering.com/community/t/1356734/pregnant-with-twins-join-the-club
and then there is this, if you do facebook:
http://www.facebook.com/groups/54450817066/
And then these have been somewhat helpful to me too:
http://www.twinparenthood.com/category/twin-tips/twin-tips-infants/
http://www.twinparents.com/articles/twin-infancy/twin-infants-sleep-and-you.html
http://www.i-am-pregnant.com/Pregnancy/calendar/twins/20-24
I have the following twin books:
Mothering Multiples (the LLL book for twins)
Ready or not here we come! (kinda silly, IMO)
Expecting twins, triplets, and quads (what most people seem to consider the best book, lots of dietary info, some helpful, some crazy insane)
Having Twins (my fave... thanks GoBecGo!)
The Everything Twins Triplets and Quads Book (pretty mainstream, but super easy to read in the bathroom)
Follow Mothering