I'm tainted by the TV show.
Bob has no face, but his voice is that of Terrance Mann.
Harry is
Paul Blackthorne.
Same here. I'll add that I usually 'hear' and envision Sanya as a taller, Russian accented version of the guy who played Morgan's TV show counterpart. TV show basically nailed my mental image of Bianca, just add fire (literally

). Morgan I tend to picture as a cross between Sean Connery and Christopher Lee, more so the latter during Turn Coat.
Other than that, I tend to picture everything animated in the art styles of the comics and book covers. Which means assigning voice actors to people instead (most of the time). Thomas usually sounds like
Steve Staley. Charity is almost
always Mary Elizabeth Glynn and Molly's usually
Kelly Sheridan. For some reason, I've taken to associating Murphy with
Maryke Hendrikse, which would be amusing as hell if you've ever seen Black Lagoon.

I've also started associating her with
Megan Hollingshead. The Senior Council members are harder to pin down -- they're all so archetypal that assigning any one person to them somehow detracts from the image.
Bears mention that I also tend to see Carlos looking something like the Jaime Reyes Blue Beetle and Mark Grayson from Invincible -- and it's a pain in the butt to find good pictures of either of them out of costume. Molly's just stuck with having blue or pink hair in every visual I have of her. And for some reason I see the Sidhe characters 'shaped' resembling Bruce Timm's art style, even when they're around others. Makes 'em creepier for one thing.
I also tend to hear Cowl's voice as if he's speaking electronically through an echo chamber. Oddly, he and Corpsetaker share a voice actor for me:
Wally Wingert, who sounds much more badass than he looks.

And yes, that includes Corpsetaker in Luccio's current body. I blame his role in Blood+.