What song was voted the best ever in the Eurovision Song Contest?

Explanation

In 2005, the EBU organised a special show to commemorate the 50th anniversary of the Eurovision Song Contest. The show, entitled "Congratulations" (after Cliff Richard´s entry for the UK in 1968) was held in Copenhagen. Many of the singers from the previous 50 years participated. A telephone vote was held to find the most popular song of all times - a vote that was won by ABBA's 1974 winning entry "Waterloo".