High value treats are usually very smelly, as in stinky, and high in protein. The highest one I have found for my dogs are the Platos salmon strips. I cut them into small pieces. I didn’t know about them until a friend in my agility class gave one to my dog - he went bonkers! They stink in my opinion, but in it sure catches my dog’s attention. I use them sparsely so they are a rare treat for my dogs.
Other good high value treat are the Natural Balance dog food rolls. You can cut them into small pieces, and freeze them. They are smelly but not nearly as much as the Platos salmon strips.
I use at least 10 different types of treats depending on the training needed, and reserve the two above for the special occasions.
My homemade Peanut Butter Bow Wow Brownies! Or the Turkey Jerky I make as well. Either goodie is like CRACK! And not just my dog, but other people’s dogs as well.
I use a microwaved hotdog- chop it up into really tiny pieces and use a paper towel to remove excess fat.
My dog is extremely food motivated and not picky at all, but I like to make sure I’m stocked with a really high-value reward for the more difficult commands!
So far, it’s been fairy successful in teaching my dog “Come.” Although right now the more effective command for come seems to be “Do you want a treat!?”
Eh, for now, I’ll take it.
When we took our Husky to obedience school, the trainer had us use small pieces of cut-up hot dogs. However, I will say that after all the sessions at the school & at home, the dog not only ended up with a serious case of the “trots”, but also stopped accepting the franks altogether. So depending on your dog’s intestinal sensitivity, you may have to either switch treats around, or find something that works for the long haul.
We use Bil-Jac with our two and they are so enthused by it that we call is Doggy Crack. They love the stuff. It is in a small freezer in the dog food section of stores that carry it.
I think Bil-Jac also makes dried & freeze-dried treats as well.
if you really want stinky + motivating, try liverwurst. It’s kind of messy, but even non-food-motivated dogs will generally do anything to get it. It’s best used in a “lick container” the dog gets to lick at, or in a “jackpot” toy the dog gets when really good and can spend some time licking at.
Or try the “mini pepperonis”, very small and smelly.
The Dog Joy soft treats they sell in some grocery stores out of a fridge case seem to be extremely motivating to many dogs.
Otherwise just use various meats- liver, chicken, roast beef, meatballs. Go visit the deli section of your grocery store and see what they have that makes your dog go WOW! this can be very dog-specific- I have one dog that LOVES triscuits, of all the weird things, and would rather get a small cracker than some string cheese or chicken.
If you want commercial treats, Bowzer’s buffalo bites are strongly scented and quite motivating to most dogs. Dog food rolls, like natural balance, are also strongly scented and motivating. You can get tripe cookies in some pet stores that stink to high heaven and dogs love them.
I actually prefer to use toys if possible and find many dogs will work harder for toys than for food, so you can explore that option if you like.
Unfortunately, this dog is not interested in toys at all. We got him when he was about 10 months old, and he didn’t play with them much then. He’s now 5, and despite the crammed-full bin of all kinds of dog toys, none of them interest him at all. We’ve tried chew toys, squeaky toys, toys with stuffing, toys without stuffing, rope toys, rubber toys, interactive toys (where he has to solve puzzles or remove smaller stuffed toys from a larger stuffed container), etc. The only thing he’ll do w/ regard to toys is try to steal them when the other dog has picked up one outside, but that’s pretty rare too, and in that case, it’s a way to get the other dog to play with him; the toy is just a prop.
Occasionally he’s interested in a plastic drink bottle, but I think that’s because he associates those with food.
At the moment, I’m using these: http://cardinalpet.com/crazydog/products/treats/train_me!_treat_bacon_flavor.html
- they come in 4 different flavors, are cheap, a little smelly, and easy to break into even smaller pieces.
Super high value (during a trial, after a run treats) are Primal Heart Chows - they’re sliced, dried lamb heart - not cheap, but my girls love them, and since we don’t use them often, the expense isn’t too bad.
We also like Lakse Kronch: http://www.sitstay.com/dog/supplies/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=39849 - they’re stinky and greasy and seem to be made of the leftovers from salmon processing (skin and bones and all), but the dogs LOVE them and the smell is powerful (stronger than the Plato’s salmon treats.)
And lots of the folks I train obedience with use the rolls of dog food, like Natural Balance: http://www.naturalbalanceinc.com/product-category.aspx?ProductCategoryID=21&category=Premium+Food+Roll+Formulas+ - they’re pretty good stuff, but you do have refrigerate them once you’ve opened them up, and that makes them less convenient for me.
You can get the Natural Balance rolls in little 99 cent sample sizes at Petco and Petsmart. The big rolls can be pricey. Freeze-dried liver gets a lot of attention at my house. I currently have some Tricky Trainers by Cloud Star that are little, extremely smelly chicken liver based treats that are a big hit, too.
My dog will eat anything, so I haven’t tried too many crazy options…but a few ideas.
It definitely on what you are doing (e.g. training/obedience and are giving many small rewards v. conformation).
For many small rewards: dry cat food, breakfast cereal (cheerios, etc.) cheese flavored crackers (goldfish or cheeze-its), Bil Jac mini sized…or make a “trail mix” of all these kinds of things so it’s always something different.
For something like conformation where a bigger, softer chunk might be easier, I have used beef jerky for people, cooked beef liver (boil first, then bake or broil to “dry”) or cheese cubes. If you have to hold it in your mouth, it helps if it’s not too disgusting (I had issues with the liver, but hot dogs were way worse!). Cheese is hard to hold in your mouth…jerky worked well but sometimes I ate it by mistake. 
