The official site of the Budapest production: Rómeó és Júlia
The official site of the Moscow production: Roméo & Juliette
The official site of the Vienna production: Romeo und Julia
A great site (in English!) about all the different productions: Romeo & Juliet: The Musicals Website
A good fan site: Roméo & Juliette
A fan site about all productions: Roméo et Juliette par Billy et Jess
And another fan site: Roméo & Juliette
Another site for the Vienna production: Romeo und Julia musical Wien