there's are hardly any American cars with V6s and manuals, but look at Japanese and European cars and the choices become more abundant.
off the top of my head, here are some cars on the used market that can be found with manuals: (some are four cyl, but have plenty of power and/or turbo)
Mercedes C-class
BMW 3 series
BMW 5 series
BMW 7 series
Subaru Impreza WRX
Saab 93 sedan, 93 hatch, 900
Saab 95, 9000
Nissan Maxima
Nissan Altima
Acura TL
Acura TSX
Acura RSX/Integra
Mazda 6
Jaguar X Type
