If you're after just bass with no guitar... that's probably going to be hard to find (on a side note, the electric bass as a lead instrument in jazz (playing the role that a guitar, sax or trumpet would normally fill) is fantastic).
For metal with very prominent bass, the main genres are death and thrash, in my experience. Tech death, especially, shows off intricate bass leads. A lot of these albums have heavy sweep picking or tapping parts from the bass. Recommendations of excellent music with prominent bass:
Necrophagist (tech death) - Epitaph
Death (death/prog death) - All albums, but primarily Human and Individual Thought Patterns, where Steve Digiorgio played for them and had a few bass solos.
Sadus (thrash) - Illusions, Swallowed in Black, A Vision of Misery. Steve Digiorgio's main band. He's very prominent, though more as a driving role with the drums than a lead role.
Iron Maiden - as mentioned already, Steve Harris is prominent and brilliant, though again in a more driving role.
Black Sabbath - Sure everyone talks about Iommi, and there's a lot of bass/guitar mirroring, but really... they're clearly bass lines that have had a chord written over them than the other way round. And listen to Bassically, the bass intro to NIB.
Dying Fetus (death) - they've got an excellent bassist, but when I saw them live, the bassist and guitarist were mirroring even when they were tapping, so you don't get to appreciate the distinctive bass sound as much.
