Heres a good size dog for you. My boy at 6 months:
http://www2.***boat.com/image_center...baloo1-med.jpg
And his Papa:
http://www2.***boat.com/image_center...butkey-med.jpg
They are Dogue De Bordeauxs (French Mastiffs). They are great family dogs. My pup and 18 month old female love the lake and to boat. The females will get about 110 to 120 lbs. and the males from 130 to 150 lbs.
Check out www.ddbs.org for a list of good breeders if you are interested.