My next A-Z list for this particular blog is Golden Age Detective Fiction Couples.
Golden Age mysteries (1920s-1950s) produced one of my favorite mixed genres: Romance and Mystery. That combo pack is still thriving today: Castle, Bones, Forever, Miss Fisher.
Golden Age mysteries not only produced memorable couples, the classic plot also required--possibly from the publishers--a "sweet young" couple who will, usually, be saved or helped or otherwise brought together while the main action is going on.
This list will address those couples, starting with A for Alleyn and Troy. 
Alleyn is an interesting example of a detective I like even though his author used him in ways that annoy me. His wife, artist Agatha Troy, is one of Marsh's most gently delineated characters. She comes across as a consistent personality--diffident, reserved, observant, careful, gently wry--and the marriage comes across in a positive light. As is customary for couples in such mysteries, she and Alleyn are involved in several mysteries together, from Artists in Crime to Final Curtain and Clutch of Constables.
Generally, however, Troy is not a fellow sleuth but an artist. Alleyn is a professional and although, like many British detectives, he gets a tad angsty, most of the time, he treats what he does as a job. Troy's avocation is treated similarly--her artist background does involve her in certain situations but always within the confines of that job.
(I think the BBC television series does a decent job. Patrick Malahide gives Alleyn slightly more whimsy. Belinda Lang is perfect as Troy. In the series, she has long hair. In the books, she has short, cropped hair. I got a picture of Belinda Lang with shorter hair.)