Allies (US/UK/USSR/France) won of course. However, most of the world benefitted indirectly from the war by moving closer to their goals.
US: Became the most important power in the world in both economic and military terms as other posters mentioned. Depression and isolationism also ended.
USSR: Once an outpost of Europe going through a destructive revolution had become the most important power in the world on par with the USA.
Western Europe: For centuries western Europe was constantly fighting and interfering in each other's affairs. There was constant mistrust and hostility. Post-WW2 Europe became the most harmonious group in the world as though a switch was suddenly turned on. Marshall plan helped modernize the economy and Bretton Woods brought currency stability.
Germany: For centuries wanted to attain parity with England and France. In the post-war period, Germany became the economic core of Europe and the defacto leader of EU - attaining Charlemagne's dream. All this achieved without picking a sword. Its people finally threw off both monarchy and dictatorship atoned for their sins and became among the most respected.
Japan: For a long time Japan was unable to come to terms with rest of Asia and was on a war course that affected both its citizens as well as rest of Asia. However, in the 3 decades post-WW2 Japan like Europe just flicked off its image switch and became an icon of peace & also the world's biggest economic superpower attaining parity with the Americans they long dreaded before the war.
Israel: WW1 already set the motion for a Jewish land in Palestine. However, the horrors of Holocaust strengthened the resolve of both Jews and rest of the world resulting in the state of Israel that was dreamed by Jews for centuries.
China: For over a century, China lived through a state of constant civil wars. The WW2 helped bring an end to that as the Communists roared through Beijing. The resulting stability catapulted China to become the most important power in Asia.
India: WW2 accelerated the freedom movement and helped the freedom cause. The post-war labor government in UK helped the transition to go peacefully and a great example of transition of power.
France: By the end of 19th century, France lost its position of a major power. End of WW2 brought back France as a major power with a seat in the UN Security Council and a major power in EU.
World institutions: For all their imperfections, the world institutions that came after the war - UN, WHO, UNESCO, World Bank, IMF did a much better job to bring the world to a single table and built international relations like no other time before.
Second world war helped fight colonialism and also brought plenty of women to the work force eventually resulted in homes with modern amenities. It also pushed for democracy and people rights significantly.
