Examples of learning by classical conditioning include Pavlov and his dogs, Little Albert, and Dr. John Garcia's experiments with taste aversion. Each experiment focused heavily on classical conditioning, especially Pavlov and his dogs, which formed the foundation for further research in that area.
Pavlov's dogs is perhaps the most famous example of classical conditioning, where Pavlov rang a bell at each meal for a group of dogs. He then found that they produced saliva after ringing the bell even without food.
Little Albert was a child who was the subject an experiment performed by Watson and Rayner in 1920, where they associated the sight of a white rat, a rabbit, a monkey and various masks with a loud noise. It was then shown later that Albert showed signs of fear even without the loud noise and in fact seemed afraid of many similar objects, including a wool coat and the family dog (a process referred to as "generalization").
Dr. John Garcia's experiments focused on associating a certain taste with an induced sickness in rats, and he found that the rats that were exposed to sickness after tasting something began to avoid that taste.