Port Aventura in Spain, near Barcelona.
Three good hotels, massive theme park, large water park.
If you stay in the hotel you get unlimited entry to the theme park and some free entry to the water park.
We have been there last two years.
http://www.portaventura.com/home.asp?pIdi=uk
Here is a map of the whole site
http://www.portaventura.es/img/mapas/uk/pa.jpg
We stayed at the El Paso Hotel which was wonderful
http://www.elalmanaque.com/turismo/portaventur a/port10.jpg