I only have 1 newfie, he's our first, and he's 9 months old. As Sarnewfie said, they are thinkers, and need stimulation for both mind and body.
Heighway, you commented that your living room looks like a Daycare center with all the toys? Here's a fun suggestion that works amazingly well in our house, and delights our friends when they come over to visit.
We made the boy-os a "Toy Box". (Actually, it's a laundry basket that we no longer use.) We put it in the living room, in the corner. We put all of the dog-toys in the basket, and have trained the boys to go to the "Toy Box" to get a toy. They'll bring the toy to us, or play with it amongst themselves. When the command "Clean Up" is given, they pick up the toy and return it to the basket. It works very well with my two older boys, Onyx is relatively new to the house, so we're still working on the "Clean Up" command, but he's got the "Toy Box" command down already.
This helps keep them thinking, as he has to decide what toy he wants to play with Mommy, and where it's at, or if he can steal it....err..... that is....creative ly appropriate it from one of his brothers, and then how to put it back.
We try and think up all sorts of new games to teach them, both to play with us, and amongst themselves. As much as I love my cuddles, I like to foster independance in them, so that if they have to be left alone, they can keep themselves entertained and not devestate my house in the process.
I've found that just about any game that you can play with a Toddleer, works (with some modifications) with a dog. I won't even go into the laugh-riot that insues when we play a game of peek-a-boo.....