Something like this? link
these guys have nice paper link
Not sure if you want printable, or printed, with photo, or the cost range, way too much interesting stuff out there. More details and we will hunt them down.
Wedding Paper Divas has an affiliate site, I think it's called Tiny Prints or something? That does adorable baby announcements. I am sure you can get to it from the WPD website.
Here we go, and they even have twin specific ones! We'll probably get ours from here because we were so happy with our wedding invites. There is usually a 10% off coupon floating around too FYI. http://www.tinyprints.com/shop/twin_birth_announcements.htm
ETA: Oops! I see someone else already posted the link. Great website though!