I use a couple different things but it depends on the dog.
Most of my Rottweilers play with the instructable dog ball (aka Bully Ball or Best Ball) which you can find here:http://www.topdogsupplies.com/store/mcart.php?ID=156
I had my last one for probably 7-8 years and gave it to a friend when I moved. Got another one recently at an agility trial. They have a cap where you can fill it with water to make it heavier to push around. My dogs usually disable the cap pretty quickly and carry it around that way. I suppose a dog could break its teeth doing that but I've used them for 4 Rottweilers so far with no issues.
The other ball I use a lot is the Jolly Ball. Not as heavy duty and a heavy chewier will go right through the handle in short time. My dogs love the satisfaction of gripping into it (versus the Bully ball that they just push around). Never had any issues but my Malinois is a little more destructive than my Rottweilers so he doesn't get to play with it unsupervised.http://www.tractorsupply.com/horse-stal ... n--5008427
My dogs have also had a great time playing with old tires from the side of the road. My male who just passed away last year LOVED to push around this big old tire. We had it hanging from a tree for awhile and he'd bark and it and push it around and eventually chewed the rope off and would roll it around the yard. You would find him wrestling with it...sometimes it would pin him and then he would flip over and pin it. He had a LOT of fun .... but I imagine a dog who was a heavy chewier would try ripping up the rubber.
I had previously used bowling balls from the thrift store but the dogs seem to have them roll and pinch their feet too much ... and basket balls/soccer balls have no longevity with my dogs.
Just some thoughts of what has worked.