Some areas of metal seem to stress clean vocals heavily, most notably heavy, progressive, and power metal, genres I have a particular love for because you can do more with clean vocals acceptably than without them (although I will listen to thrash & death metal on occasion). Power & progressive metal are more technical than the other genres, and focus on song concept more than what is found in most other genres across the board since metal fans have some of the most contentious standards for music in general out there.
To Azul though, better examples of metal IMO (at least, the generally more popular subgenres of metal) are
(Angra - Nova Era),
(Kamelot - Memento Mori), http://www.youtube.com/watch?v=fJVQP108eM4 (Dream Theater - Under a Glass Moon), http://www.youtube.com/watch?v=aw77gNrwyr8 (Symphony X - The Odyssey; this is only largely the first 9 minutes of the song - the original song is ~24 minutes long, and unlike most that long, it is a memorable song).