For a really filthy groove a dual or triple bass attack is a must - any combo of Larry Graham, Bootsy Collins, Mark King, Stanley Clarke, Les Claypool and Louis Johnson.
Twin drums and percussion - Dave Garibaldi from Tower of Power and Tony Thompson
Guitar - someone who can play restrained funky rhythm and shred when called for. Satch is the man.
Keyboards - Bernie Worrall no question.
Vocals - most of my favourite singers are long gone dead or getting that way. of those living and youngish, Mike Patton'd be #1. plus several attractive ladeez on backing vox e.g. Britney, Shania, Beyonce Knowles.