How do I love thee? Let me count the ways. My favorites are the Lord Peter/Harriet Vane combos:
Strong Poison Dorothy Sayers's Lord Peter Wimsey ranks among the world's great fictional detectives. In this story he joins forces for the first time with the one true love of his life, Harriet Vane, who is on trial for poisoning her fiancé when Wimsey meets her. Not only does Wimsey believe in her innocence, he falls in love with her at first sight. Cleverly he brings home the case for her.
Have His Carcase The mystery writer Harriet Vane, recovering from an unhappy love affair and its aftermath, seeks solace on a barren beach -- deserted but for the body of a bearded young man with his throat cut. From the moment she photographs the corpse, which soon disappears with the tide, she is puzzled by a mystery that might have been suicide, murder or a political plot. With the appearance of her dear friend Lord Peter Wimsey, she finds a reason for detective pursuit -- as only the two of them can pursue it.
Gaudy Night When Harriet Vane attends her Oxford reunion, known as the "Gaudy," the prim academic setting is haunted by a rash of bizarre pranks: scrawled obsentities, burnt effigies and poison-pen letters -- including one that says, "Ask your boyfriend with the title if he likes arsenic in his soup." Some of the notes threaten murder; all are perfectly ghastly; yet in spite of their scurrilous nature, all are perfectly worded. And Harriet finds herself ensnared in a nightmare of romance and terror, with only the tiniest shreds of clues to challenge her powers of detection, and those of her paramour, Lord Peter Wimsey.