Well we went to Polperro (obviously!), Tintagel, Bedruthan Steps, Newquay, Land's End, St Michael's Mount, St Ives, Truro, Dartmeet, Dartmoor, Salcombe, Burgh Island and Looe. Didn't we fit a lot in?
Of the places we didn't go, top of my list in Cornwall would be Mevagissey and Fowey on the south coast; they were affected by the flood just before we went and that's why we didn't go there. They are pretty close to Polperro otherwise. Then on the north coast Padstow and Rock are meant to be pretty HIP now and I would have gone there had we more time!
In terms of Devon, I love the North coast around Croyde, Ilfracombe, Clovelly and Westward Ho! way; it's just that that's quite a drive around Dartmoor from where we were. On the South coast, I think we saw the best of what there is in southwest Devon, but if you're willing to go further into Devon, then Teignmouth, Torquay, Brixham, Paignton, Seaton and Sidmouth are all lovely little towns with beaches and/or harbours.