Lordi's "Hard Rock Hallelujah"
Finland's demon-dressing 2006 entry, Lordi, was so popular it actually won the whole contest. At the time, it received the most points, ever (alas, that record was beaten three years later).
The band's popularity continued beyond the contest. When "Hard Rock Hallelujah" was later released as a single, it made it to number 25 in the UK Top 40. And when 80,000 people sang it in Helsinki's Market Square, they broke a karaoke world record.