Hrm. I read the DN manga before watching the anime, so I had a slightly different voice in mind for Mello and both startled me a bit. The closest VA was Nozomu Sasaki, who was pretty spot on aside from sounding older than I'd imagined (which makes sense, considering he was 39 at the time).

His other roles include:
-Tetsuo (Akira)
-Eriol Hiiragizawa (Cardcaptor Sakura)
-Hayate Gekko (Naruto)
-Shadi (Yu-Gi-Oh! Duel Monsters)
-Yusuke Urameshi (YuYu Hakusho)

And a bunch of others, listed here (http://en.wikipedia.org/wiki/Nozomu_Sasaki).