Even though it can be a rather cliched plot device, I tend to like stories in which a character suffers from some kind of memory loss. In each of these romance, one of the protagonists is dealing with either partial or full amnesia.

Come Love a Stranger
Embracing Death
Father, Unknown (Harlequin SuperRomance #784)
Feeling Death
Grayson Prentiss's Seduction
Great Scottish Devil, The
Night Storm
Return of Chase Cordell, The (Harlequin Historical #348)
Some Enchanted Season
Someone to Watch Over Me
Tucker's Claim
Very Vampy Christmas, A
What the Bride Didn't Know (Harlequin Kiss #38)
Witness, The