Sparhawk from The Elenium calls anyone he didn't know very well as "neighbor." He says he's just trying to be friendly. When asked why he doesn't just call them friend, he says that they aren't actually his friend yet, so he doesn't know if he'll have to kill them at some point.
Sartain Stradius from Felsic Current, says "See" at the beginning of sentences, or at the end, or after a comma. Anywhere. And often, see.
Mariana from Icarus Phaethon's The First Breath, with her idiosyncratic habit of beginning her sentences with "Aha".
Padfoot in Summerland interjects his chuckle, described as paper dry, into almost everything he says.
Hasimir Fenring of Frank Herbert's Dune tends to pepper his dialog with phrases such as "hmmmm" and "hmmmm-aaah" for no apparent reason. However, this is actually a plot point - Fenring and his wife have a private code disguised as humming, allowing them to hide a conversation with one another in the midst of an overt conversation with someone else. However, it sounds like a verbal tic to other characters.
Carcer Dun of Night Watch is arguably one of these - he punctuates his speech with an "irritatingly patronising chortle", which is always rendered in the text as "haha." We also have Captain Tilden, what. And Snouty, hnah. Captain Swing also exhibits afunnyway...of speaking.
Brother Nhumrod of Small Gods has a habit of repeating the last few words of the previous speaker. Many of Terry Pratchett's characters (especially his villains) have this sort of verbal tic, whether by the in-sertion of mispla-ced pauses orbyhaving... the speedof the... words be . . . curiouslyrandom or just by using a lot of —ing Unusual Euphemisms.
In Snuff, Lord Rust has picked up a habit of adding "what" to the end of sentences. It annoys Vimes greatly.
In the third book of The Chronicles of Narnia, it was established that Calormenes always follow any mention of the Tisroc note May he live forever. with the phrase "May he live forever", usually rendered in parentheses to indicate just how unconscious it is. When talking horse Bree omits this little phrase, the protagonist rather nervously calls him on it, to which the horse replies: "Why should I say that, when he won't live forever and I don't want him to anyway?"
Professor Umbridge in Harry Potter frequently clears her throat (usually to interrupt someone), rendered as "hem hem." And then there's Ron's "Bloody hell!"
Gollum in The Hobbit and The Lord of the Rings. In this case, the character is actually named after his catchphrase. He also addresses his words to the Precccioussssss frequently.
Jacob Two-Two, because he has two brothers and two sisters and two parents, yes, two brothers, two sisters, and two parents, says everything twice. He says everything two times. Nobody ever hears him the first time. No, nobody ever hears him the first time.
Offscreen, in Spider Robinson's novel Stardance: the narrator mentions a character who unthinkingly replies "There you go" to everything anyone says. By the end of their acquaintance, the narrator is considering dumping him out an airlock. "There he goes, I kept thinking, there he goes ... "
Shirley Jackson, in her loosely autobiographical Raising Demons, describes her daughter Sally going through a phase, at about four, where she repeated the key word in every sentence: "Well, I told Amy's mother that I did not have any breakfast, breakfast, because my mommy did not wake up and give it to me, mommy. And Amy's mother said I was a poor baby, baby, and she gave me cereal and fruit, cereal, and she said there, dear, and she gave me chocolate milk, and I did remember to say thank you, remember." (Jackson was gifted at capturing the Verbal Tic s of small children's speech: "You bad bad webbis.")
J.R.Ward's Black Dagger Brotherhood character, Vishous tends to substitute other words with, "true" or otherwise use the word as a sentence-closer; "You've got my back, true?" or "We'll get this done, true."