Depends where you are. It takes ages to get from North coast to south coast.
If on north coast, then:
Clovelly is an amazing place. Picturesque village on the side of a steep cliff, with old-world fisherman's houses and donkeys used to deliver peoples shopping because it is too steep for cars. Well worth going. You need to be fit to walk up again.
Lynton & Lynmouth are really nice villages to visit.
Appledoor is nice.
Exmoor and Dartmoor are nice. Loads of hills and walks around there.
South coast Devon I know less. Looe and Polperro are just over the border into Cornwall, and are really nice places.