The legacy ICANN/NSI set are the most well-known namespace on the Net, as they are the current extension of the original monolithic DNS system. OpenNIC's position on these TLDs and their registrars is that, for the sake of tradition and historical continuity, it would be inapopropriate to establish a TLD in conflict with them. A complete alphabetical list of TLDs in use by ICANN is available on IANA (ICANN)'s website here.
Traditionally, the two-character TLDs have been reserved for demarcation by political unit, the top level being reserved for coutries as designated by the International Standards Organization (ISO). OpenNIC will not establish any two-character TLDs, since countries come and go and ISO needs to be free to designate new country codes for them. The ISO country-code list are available from ISO at http://www.iso.ch or can be read online at http://www.bcpl.net/~jspath/isocodes.html.
There were seven global TLDs designated at the beginning of the DNS system. Three of these were given to Network Solutions, Inc. and, more recently, to ICANN:
The other four are administered seperately by their own NICs:
ICANN then approved more gTLDs for inclusion in the ICANN-controlled DNS namespace:
ICANN has been accepting and approving thousands of "New gTLDs" that various companies and registries can apply for ownership of. The complete list of delegated strings can be found at newgtlds.icann.org (they would be too numerous to list on this page).