Well, since FUBAR was the only one who mentioned him, I'll go ahead and scream DEVIN TOWNSEND. It's really odd that no one else has mentioned him, since he's easily one of the best vocalists in metal.
Other than him....
Hansi Kürsch (Blind Guardian) - No one sounds like him.
Jonas Renkse (Katatonia, ex-October Tide, backup vocals in Bloodbath) - THE voice of depression.
Mikael Åkerfeldt - No need to explain.
Warrel Dane (Nevermore, ex-Sanctuary) - Very edgy voice, and very emotional.
Russell Allen (Symphony X, guest vocals on various other things) - His voice just soars, and can be very emotional.
Vincent Cavanagh (Anathema) - His clean vocals are so understated yet emotional.
Ihsahn (Emperor, Thou Shalt Suffer) - His screams were unbelievable, and he was developing quite a singing voice by the end of Emperor.
Vintersorg (Vintersorg, Borknagar, Fission, ex-Otyg, Waterfield, ex-Masticator) - Good black metal vocals, incredible clean vocals.