I'd like to suggest:
Harry Kemelman's books staring Rabbi David Small
Brian Freeman's Jonathan Stride series
Laurell K. Hamilton's Anita Blake (erotic magic-oriented detective series of a sort)
J. A. Konrath's Jack Daniels series (see his
blog for great commentary on ebooks/drm/etc)
Gregory McDonald's Fletch series.
Douglas Preston & Lincoln Child's Pendergast series.
The Amelia Peabody series by
Elizabeth Peters.
Ridley Pearson's Boldt/Matthews series.
I'm sure someone's mentioned The No.1 Ladies series...it's on my list to read after having loved the BBC series of the same name.
And I have a nostalgic memory for the Hardy Boys and Tom Swift/Tom Swift Jr. books.