CW says, "Actually, according to Jim Dale, the actor who reads the audio books for the US, there are over 200 characters who require voices."

Well, this is something to be checked, is it not? I scanned through book one, looking for quotation marks, and if I count aright there are 64 voices just in that book.

Here's the list: first more-or-less major characters alphabetically (so they can be easily found as we check later books), and then minor ones in rough order-of speaking. Numbers give the page where the person first speaks and, where first mentioned or identified.

Albus Dumbledore 8
Dursleys: Vernon 2 Petunia 7 Dudley 21
Argus Filch 127 157
Seamus Finnigan 121 124
Prof. Flitwick 138 165
Hermione Granger 105
Rubeus Hagrid 14
Madam Hooch 127 146
Lee Jordan 153 188
Neville Longbottom 94
Draco Malfoy 77 108
Minerva McGonnagall 9
Madam Pomfrey 12 301
Parvati Patil 121 147
Madam Pince 198
Harry Potter 15 19
Professor Quirrell 70
Severus Snape 126 136
Dean Thomas 121 187
Weasleys: Molly 91; Fred, George, Ginny 92; Ron 93; Percy 92 96
Oliver Wood 151
Voldemort 11 (speaks much later, in turban)

persons #1 & #2 on street 4, wizard in violet cloak 5
radio: newscaster Ted & weatherman Jim McGuffin 6
Dedalus Dingle 10 69
zoo incident: snake 27, Piers Polkiss 23 28, reptile-house keeper 29
hotel owner 42
L.Cauldron: landlord Tom, Doris Crockford, 2 unnamed wizards 68-69
Diagon Alley: unnamed goblin, Griphook 73, Madam Malkin 77, Mr. Ollivander 82
train: Grandma Longbottom 94, sandwich seller 101, conductor 110
ghosts: Fat Frier 115, Nearly Headless Nick 115 124, Peeves 115 129
Sorting Hat 117, portrait lady 129, ~3 whispering students 131, chessmen 199
centaurs Ronan, Bane, Firenze 252-56
Ron imitates Hermione 269; Harry imitates Bloody Baron 274

I'm almost done with the further names in Book Two. Anyone want to tackle a later book?