We have a lab, and I couldn't recommend them more highly.
Our dog is an angel and a joy to have around....
as with all the other posts, I agree, dogs take up a lot of time and energy and any large-ish breed is going to require exercise daily, otherwise they'll be bouncing off walls in no time!!!
I would say, if you get a puppy, get a crate for them... I didn't agree with them, until I got my puppy, but the crate really helped with housetraining, was somewhere safe I could put the puppy and, as we found out, was somewhere he went when he wanted some peace and quiet from the kids. We never used it as punishment, and he loved sleeping in there (not as much as he loves sleeping on the bed now, when he gets the chance... !)
I can honestly say I don't have a single doubt about him being great with the new baby. Not one.
So, I'd vote for a lab, and I'd also bote for getting a puppy from a registered breeder, as there is less chance of problems around the kids (a good breeder will let you take the kids to meet the bitch and the puppy before you sign on the line!!) but I am sure most other breeds are OK too... I have heard some bad press about dalmations - they are not as placid as people like to think and aren't always best placed with little kids.
I hope you get to choose your puppy soon!!!
K x