At the B&N Reads blog he tagged the top six unrequited loves in literary history, including:
Jane Austen and Tom LefroyRead about the other entries on the list.
No one can prove that Jane Austen was hopelessly in love with Tom Lefroy, or that Lefroy was the inspiration for Mr. Darcy, or anything beyond the documented facts that Austen and Lefroy flirted a bit and had some sort of go-nowhere relationship. The circumstantial evidence is powerful, however: Austen wrote three novels in a furiously passionate period immediately following her time with Lefroy, hinting at some sort of powerful emotional event—like, say, the man you’d fallen in love with leaving you to pursue (an admittedly brilliant) legal career.
Also see John Mullan's ten best examples of unrequited love in literature.
--Marshal Zeringue