Excellent reply. You covered all the points I had in mind.
Kongs are a fantastic toy. I personally keep my house littered with bones. Baked cow femurs, baked and bleached cow bone bits, nylabones, and even the "stuffed" bones you see at Petco.
My favorite thing to do for bored-during-the-work-day dogs, was to take half their ration of kibble and spread it out through the kongs, like Stalk suggested, and a handful of the rest of their food and hide it throughout the house in places that would require a dog to use his brain, but not his mouth, to get to. Under tables blocked off with chairs, under the armoir, under the coffee table, behind the lamp-table, etc. and scatter some just around the floor. Sure keeps a dog busy.
Also, a couple really fun toys I found were the "talk-to-me treat ball" where you record your own voice, or any noise at all, saying something. Then you pack it full of easily-tumbled-out treats, turn it on, and leaves it on the floor. Whenever the dog touches it, it says the phrase or makes the sound. When the dog rolls it, treats fall out.
For a more complex toy, consider the Buster Cube. It has various levels of difficulty, and can function even after aggressive chewing. The more the dog tumbles, the more likely it is a treat will fall out of it. a treat will not always fall out, so the dog has to keep tumbling and rolling it around. My dogs loved that thing. I still have it, somewhere. It got "lost" when we moved. :\
