Breath - some diseases, like kidney failure and diabetes, can cause a change in breath.
Diseased teeth and gums - dental disease and infected gums can produce a very foul odor. Additionally, a sore mouth may cause increased drooling. The malodorous saliva can coat the fur, furniture, etc., and you may not recognize that this is originating in the mouth.
Infected ears - bacterial infections of the ears are often extremely smelly. Vets often diagnose this type of infection by smell upon entering the exam room. Your dog will usually be scratching or shaking the head, but not always. A bath may make ears worse if water is trapped in the ear canal.
Flatulence - is the odor on your dog, or from your dog? Flatulence, or "gas" may indicate a dietary or intestinal problem. Some flatulence is normal, but if this is regularly occurring, please see your veterinarian.
Anal glands/sacs - this is perhaps the most common cause of doggie odor that won't go away. Anal sacs are two small scent-sacs in the area of the anus. These are a type of "marking" glands. When a dog has a bowel movement, these sacs are normally squeeze, and a very smelly, oily secretion is released with the feces.
If these sacs become infected or impacted (thicker secretion than normal, can't empty properly), problems result. This can be a very painful situation when they become infected! If a dog (or cat) is scared or overly excited, these glands can secrete the smelly, oily substance on the surrounding fur, causing bad odor.