Two good choices would be Wuthering Heights by Emily Bronte and Jane Eyre by Charlotte Bronte. While The Castle of Otranto was the novel that kicked off the English Gothic genre, you might find it difficult and rather boring. It was written in 1765, which makes it quite old. The Brontes wrote in the 1800s.

Wuthering Heights is probably the more truly Gothic of the two, but both contain strong Gothic elements. Wuthering Heights offers the classic Byronic hero in Heathcliff, who is one of literature's more notable leading men. The haunting setting of the English moors is prevalent in Emily's work, and the supernatural element is definitely stronger in Emily's work than in Charlotte's.

Jane Eyre has a lot to recommend it. The heroine is more likable than Catherine from Wuthering Heights. While Mr. Rochester is not as tormented as Heathcliff, he definitely qualifies as a Byronic hero. While the moors are not as important in Jane Eyre as they are in Wuthering Heights, the large country house with the forbidden wing presents the classic Gothic setting perfectly. Although the supernatural element isn't as strong, dark secrets, mental illness, and tragedy make up for that.

Either Wuthering Heights or Jane Eyre would be an excellent choice. Both are classics that have been written about by scholars and critics for decades. Either one would be interesting and provide many angles from which to write your research paper.

Which interesting Gothic novel, besides Frankenstein, Dracula, or Twilight, should I choose for my research paper?

In concurrence with Post #4 The Castle of Otranto is defined as the first work of gothic literature, so it would, indeed, provide an excellent topic for research.  And, along with Post #5 is Jane Eyre by Charlott Bronte.

Nathaniel Hawthorne's The House of Seven Gables is, of course, a classic gothic novel, which much written about it.  And, while it is not classified as gothic, per se, Victor Hugo's Notre Dame de Paris, The Hunchback of Notre Dame can easily be defined as a gothic novel, and is great reading by one of France's greatest writers.  In it is the psychologically deranged bishop, the grotesque Quasimodo, the dark, foreboding cathedral, the crimes, etc.

I'm casting my vote for Frankenstein (which, of course, you've excluded) or The Picture of Dorian Gray.  Both of these are among my favorites--they both focus on imagination, the supernatural, the individual rather than society as a whole, nature, and emotion rather than reason.  I think you'd really enjoy both of these stories, and you will not have any trouble finding sources for either of them.

I like the Southern Gothics myself: Flannery O'Connor and William Faulkner, chief of these.  As I Lay Dying (1930) is a great book.  As is Wise Blood (1952) by O'Connor.

Both focus on death: physical, spiritual, and emotional.  There's hauntings, blindings, smelly corpses, hell on wheels.

For more mystery, Rebecca (1938) by Daphne Du Maurier is a classic.  It's a classic ghost story.

If you have an interest in modern fiction and vampires but want something with more substance than the Twilight series, I suggest that you take a look at anything by Anne Rice. Her Vampire series (Lestat) and her Mayfair Witches series both have a great deal of depth in terms of plot development, literary value, and social significance.

Also, staying 20th century, another good choice would be H.P. Lovecraft.

For American canon authors, I would definitely look at Poe.

Any of these are readily researchable.

You could also try The Castle of Otranto by Horace Walpole.  It is brief; so you could read it quickly and is considered to be the first Gothic novel published in the English language.  Because of its early publishing date (1765), many future Gothic works emulated the motifs and archetypes used by Walpole.

I read the book for grad school and remember enjoying it because it is so over the top.  You should be able to find a significant amount of research and criticism for Castle, and because it is not as well known as other Gothic works (especially American ones), you might be the only one who chooses it.

This is completely my personal choice but you might enjoy reading The Picture of Dorian Gray by Oscar Wilde.

One interesting thing about this novel is that the main character, a VERY attractive young man, effects a strange attraction on the man who is painting him -to the point of near obsession.  The interaction among the male characters is quite interesting and leads to questions which, coincidentally, were also asked to Oscar Wilde before sending him to jail for 2 years for homosexual acts in 1895.

Another interesting fact is the gothic element: The picture begins to change, age, deform, and becomes grotesque- at the same time, Dorian remains beautiful, young, and still causing havoc amongs people.  We learn that his soul was indeed transferred into the picture and that all that lives inside his soul is reflected in the face of the painting: His inner evil, his debauchery, the way he ruined a few men in London (we never know how in the story, but it is hinted), and the fact that he drove a woman, his only "love" to suicide.

As far as sources, you may find a lot of interesting information on Dorian Gray in the Oscar Wilde Web.

Wilde actually based Dorian's character on a friend of his, John Gray, who was one of Oscar's closest companions-and one very handsome too.

Another thing is that when this novel came out, it flat out outraged Victorian society, and Wilde was called everything in the book. This was a sign of things to come- shortly after more plays in which Wilde employed more "dandy" characters began to create a portfolio in the eyes of the hypocritical London society, and people wanted to see him burn for what they thought was his tendency to be immoral. In fact, they did.