Ooh I'm glad of this question, I'm doing history GCSE and I need to brush up a little.
The main effects of WW2 were a significant loss of soldiers, equipment and an enormous war bill. The atomic bombs dropped on Hiroshima and Nakasaki had an effect as well; making generations of innocent people genetically mutated and flawed.
A huge influx of immigrants, mostly Jews, blacks and anyone not "perfect" in the eyes of Nazi Germany into Great Britain.
However, there were also several positive effects. During the war, American and British people became closer because of the ridiculous amount of GI's shipped to Britain. (There is an old saying about the GI's that was often coined by British men: "Overpaid, oversexed and over here")
Also, Hitler and the Nazi leaders all either committed suicide or were executed as war criminals.
An important thing to note is that Nazi scientists performed horrific testing on Jewish people, mostly twins, dwarfs and similar. However, that did not stop America giving them amnesty in return for their work with the US government on developing the Atom Bomb.
That's about all I can remember right now. Guess I need to revise...