Devon
Dartmoor - natural, too many spots to mention
Exmouth - natural & street (need to check tide times as if its high it will cut off the rocks)
Dawlish - natural
Teignmouth - street
Plymouth - street & natural down at the Hoe
Minions Quarry - natural
Torquay - natural, loads of coastal rocks
Cornwall
Looe - street & some natural
Cligga Head (nr perranporth) - sick street/natural
Wheale Kitty (sp? nr St Agnes) - street
Lamorna Cove - natural (best place in the world )
Some of the Cornish lot will add to that list as there are more places i've ridden there but can't remember the names/locations