I personally only watch the Eurovision Song Contest for fun and not because I like the music. But since it's the time of year for the 2008 final I'll take a look back in the history of dancemusic in the Eurovision.
Most dancemusic on the Eurovision have been second rate versions of the real thing, just like rock, pop etc. on the Eurovision mostly is second rate. But thanks to the popular tv-show we all get an insight to the musical culture across Europe (and beyond nowadays). And once in a while we do get some gems out of all the efforts.
In recent years established artists have started to appear more and more frequently. In 2004 both E-type and Scooter entered the local Swedish and German competitions. None of them went on to the international show and the songs isn't among the best material from eithers back catalogue but both with their unique sound and Scooter ending at a respectable 2. place in Germany with "Jigga Jigga".
Often you have to look at the local competitions to find the best dance songs like The Attic's "The Arrival" posted earlier. But you'll also find something good in the international, most notably Antique's "(I Would) Die For You".
And now a true 90's classic Gina G's "Ooh Aah ... Just A Little Bit" which launched Gina G into a short but big career with many hits. Most people outside the UK probably don't even remember the song as a Eurovision song as it for some reason only ended as #8.