Open Moorland
There is a network of bridleways that criss cross dartmoor providing riding for all abilities. The guide book South West Mountain Biking: Quantocks, Exmoor, Dartmoor contains a good selection of rides.
{TODO: Links to PDFs of routes.}
Trail Centres
Haldon Forest Park provides purpose built cross country trails at a beginner and intermediate level, including cafe, toilets and bike hire.
Devon's official downhill venue at Gawton, Requires Woodland Riders membership, daily rate available.
Cycle Routes
The Granite Way [PDF] - Okehampton to Lydford, is a 11mile ride that provides stunning views from a well surfaced path. This is part of the longer Devon Coast to Coast route.