According to the Romance Writers of America, every good romance needs these two things:
A Central Love Story: The main plot centers around individuals falling in love and struggling to make the relationship work. A writer can include endless subplots, as long as the love story is the main focus of the novel.
An Emotionally Satisfying and Optimistic Ending: In a romance, the lovers who risk and struggle for each other and their relationship are rewarded with emotional justice and unconditional love.
On this page, you'll find plenty of books that match this description. For each subgenre (YA, Historical, Contemporary, Paranormal, and Romantic Suspense) you'll find a short description as well as several books that are representative of the subgenre.
Listed below are links to the webpages of some of the most popular romance writers.