MC Beaton, Hiiassen, and I agree Evanovitch definitely! (grandma Mazur, Lulu and Bob the dog - the scene where she got Bob to poop on her arch enemy's lawn had me absolutely rolling!).
Another favourite, Elizabeth Peters with her Vicky Bliss series as well as her character Jacqueline Kirby (a librarian). I am not so fond of Ameilia Peabody any more, although I really enjoyed her first 2 or 3.
I will read anything by Joan Hess - she has 2 series - the Maggody Mysteries (Arlie Hanks is the woman sherrif and apparently the only sane person in Maggody - a hick town like Hooterville in the Ozarks) and her Claire Malloy series - a book seller with a teen age daughter - these are laugh out loud funny.
I also adore the character Marcus Didius Falco who is an "informer" in Rome around 70 AD or so, by author Lindsay Davis. They are brilliant and Falco is as wise cracking as any PI today.
I've recently stumbled across the "Miss Zukas" mysteries by Jo Derske (sp?) She is a librarian and since I have worked in libraries I found them very amusing (not slap your knee funny just bright and witty).