European postal administration who don't issue Europa stamps (for the moment) :
Alderney is part of the Bailiwick of Guernsey and its stamps are valid throughout the Bailiwick. Stamps issuing since 1983.
official website: http://www.guernseystamps.com
State website: http://www.alderney.gov.gg/stamps/
2. Mount Athos - [Hagion Oros]
In 2008 the Hellenic Postal Service started issuing postage stamps for postal use only at the two post offices of Mount Athos (Karyai and Dafni). The first set of 5 stamps was issued on May 16, 2008. The Hellenic Post issues the modern era Mount Athos stamps despite opposition from the Philatelic Federation and the Hellenic Philatelic Society.
official website: http://www.agionorostamps.gr
3. Sovereign Military Order of Malta - [SMOM]
The stamps are issued for both postal and charitable reasons. Despite over 50 bi-lateral postal agreements the stamps are usually classed as cinderella stamps as they do not have postal validity throughout the world. Most postal agreements are with countries in which the order does charitable work.
official website: http://www.orderofmalta.org
4. United Nations Postal Administration (UNPA) - European offices in Geneva and Vienna
The idea for the UN to issue stamps originated in 1947 with José Arce the ambassador from Argentina and president of the United Nations General Assembly, who was himself a philatelist. (The League of Nations had used overprinted Swiss stamps.) The UNPA came into existence by agreement with the U.S. in 1951, soon after the UN moved into its headquarters in Manhattan. Prior to that, the UN used the facilities of the United States Post Office Department.
Ordinarily, mail must be taken to the UN offices and franked with the appropriate UN stamps. From time to time, though, by agreement with the United States Postal Service, the UNPA maintains a temporary office elsewhere, usually at stamp shows or special events.
official website: http://unstamps.un.org
official website - Geneva: http://unstamps.un.org
official website - Vienna: http://unstamps.un.org