I met a shocking (for me) information, that Germany and Poland have not signed a peace treaty after the World War II.
Because I could not believe this, I performed some research.
In the Potsdam agreement:
The three Heads of Government reaffirm their opinion that the final delimitation of the western frontier of Poland should await the peace settlement. The three Heads of Government agree that, pending the final determination of Poland's western frontier, the former German territories cast of a line running from the Baltic Sea immediately west of Swinamunde, and thence along the Oder River to the confluence of the western Neisse River and along the Western Neisse to the Czechoslovak frontier, (...), shall be under the administration of the Polish State and for such purposes should not be considered as part of the Soviet zone of occupation in Germany.
This was however not signed neither by Germany nor Poland.
The similar question was asked on wiki.answers.com:
Basically a formal state of war existed between Germany and the various Allied nations until about 1949 although obviously all combat operations had ended many years previously. By 1954, Stalin was dead, the German government reorganized (east and west), and the German economy stabilized and growing. POWs, both German and Japanese were just being released about this time in large numbers by the Soviets.
Although I've never seen a full reckoning I suspect some nations never actually signed a treaty ending the war with Germany - for examples, perhaps Brazil or Costa Rica.
(...) A treaty between the (main) Allies and Germany was signed on 12 September 1990 just before the re-unification of Germany. This was essential in order to make Germany's new frontiers definitive. It was agreed between the four main Allies on the one hand and the two German states on the other, with the proviso that it wouldn't become fully effective unless ratified by the new, united Germany.
This treaty is regarded by Germans as equivalent to a peace treaty. A comprehensive treaty would raise all kinds of problems in respect of countries that were British and French colonies in WW2 but are now independent.
Already in 1947 the Allies issued a solemn statement to the effect that they were no longer at war with Germany.
Poland and East Germany were vassal states of the Soviet Union, and we can consider also (in this subject) West Germany as a puppet of the USA. Soviet Union had no problem if they had no peace treaty because she controlled them both (USSR however did, see below). But in 1990 Poland was no more a Soviet bloc member and signed a border treaty with (Federal Republic of) Germany (source):
Article 1. The Contracting Parties reaffirm the frontier between them, whose course is defined in the Agreement between the Polish Republic and the German Democratic Republic concerning the demarcation of the established and existing Polish-German State frontier of 6 July 1950 and agreements concluded with a view to implementing and supplementing the Agreement (Instrument confirming the demarcation of the State frontier between Poland and Germany of 27 January 1951; Agreement between the Polish People's Republic and the German Democratic Republic regarding the delimitation of the sea areas in the Oder Bay of 22 May 1989), as well as the Agreement between the Polish People's Republic and the Federal Republic of Germany concerning the basis for normalization of their mutual relations of 7 December 1970.
This is not a peace treaty, so I looked for documents mentioned there.
The treaty of Zgorzelec (the one between Poland and the DDR)
was worded as a declaration and was not recognised as a legitimate international treaty by West Germany insisting on its exclusive mandate and the members states of the NATO. Four years later when the Soviet Union granted East Germany independence, the Soviet Union reserved rights over East Germany (similar to the rights reserved by the Western Allies over the West Germany under the Bonn–Paris conventions) pending a final peace treaty with Germany - the 1990 Treaty on the Final Settlement with Respect to Germany. So although the treaty was binding on the two states it was not seen by many western members of the international community as a definitive.
The treaty of Warsaw (the one between Poland and BRD)
In the treaty, both sides committed themselves to nonviolence and accepted the existing border—the Oder-Neisse line, imposed on Germany by the Allied powers at the 1945 Potsdam Conference following the end of World War II. (...)
At the time the treaty was signed, it was not seen as the last word on the Polish border in West Germany, because Article IV of this treaty stated that previous treaties like the Potsdam Agreement were not superseded by this latest agreement, so the provisions of this treaty could be changed by a final peace treaty between Germany and the Allies of World War II—as provided for in the Potsdam Agreement.
As I understand, there really was no document between Poland and Germany that bore the name "peace treaty". However, it seems there were no direct "peace treaty" with anybody else; should then "4+2" agreement be considered as a peace treaty of WW2?