What is standard of proof for conviction of a crime?

One of the most common concepts in criminal law is the presumption of innocence.  Any loyal television viewer of Law and Order has heard this a thousand times.  In Georgia OCGA Section 16-1-5 defines the   standard of proof for conviction:

 
Every person is presumed innocent until proved guilty. No person shall be convicted of a crime unless each element of such crime is proved beyond a reasonable doubt.