The IETF is an important Internet standards body. IETF is a short name for “Internet Engineering Task Force”. The IETF is responsible for the creation of RFCs. Unlike other, formal standards bodies it is loosely organized. There is no specific membership to the IETF, anyone (knowledgable) can become an IETF member just by paritcipating on the IETF discussion mailing lists.
The IETF itself provides a good overview over itself at http://www.ietf.org/about/.