Frank Muller was wonderful.
George Guidall - who has narrated over 1,200 audiobooks, evidently, and who replaced Muller on King's The Dark Tower books after Muller's passing - is brilliant, IMO. Probably my go-to narrator (if I see him listed on an interesting-sounding audiobook, I will consider getting the book). He has a voice full of character.
Guidall is from the U.S., though... not sure if you're looking for a Brit? If so, I think John Lee - who has narrated a bunch of Alastair Reynolds novels - is excellent. He also does straight history books... I have a few by him and he seems quite good at these, too. He has a great voice, like a classically trained actor.
Just a few off the top of my head, CC
edit to add: Sophie Aldred - who narrated the books of Tchaikovsky's The Final Architecture series - is terrific. Gravitas galore, IMO, and does wonderfully diverse character readings.