NIST National Institute of Standards and Technology:
http://csrc.nist.gov/publications/PubsFIPS.html
http://www.itl.nist.gov/fipspubs/by-num.htm
http://csrc.nist.gov/groups/STM/cavp/documents/dss/ecdsaval.html
http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf

SECG The Standards for Efficient Cryptography Group:
http://www.secg.org/
http://www.secg.org/?action=secg,docs_secg

IEEE Institute of Electrical and Electronics Engineers
http://grouper.ieee.org/groups/1363/
http://grouper.ieee.org/groups/1363/P1363/index.html

X9 Accredited Standards Committee Financial Industry Standards
http://www.x9.org/home
http://www.x9.org/standards/free/TG26_1999.pdf