Two songs that sounds almost the exact same are AC/DECs "TNT" and Lou Gramms "Arrow through your heart". AC/DC came out with the song first which would lead people to think that Lou Gramm copied them and used the beginning of the song in his. So the next time you listen to these songs, pay attention to the beginnings and you'll notice they sound the same.

https://www.youtube.com/watch?v=adukrwHY09s

Two songs that sound similar but may not be copy righted are Star Wars's "imperial march" and Mary Poppins "Spoon full of sugar". It transitions from instrument to voice with the high point of the imperial march going with the chorus of a spoon full of sugar when she says "A spoon full of sugar makes the medicine go down."

http://www.soundsjustlike.com/2720/john-williams-sounds-like-walt-disney/