ACCF/AHA guidelines - nice summary of current thoughts.
Similar guidelines were published recently by the European Society of Cardiology.
Images above show non-invasive cardiac imaging using CT, compared (bottom) to invasive coronary angiography - 'A'. Note the distal left main stem 'soft' plaque visible on the contrast CT - 'C', invisible on the non-contrast calcium scoring CT scan in 'B'.
Dangerous plaques are missed by calcium scoring alone in maybe 5% scans in symptomatic subjects.