Books of course have nearly every trope imaginable, but also (nearly always) have far smaller audiences. So let us deal with film and television.
Here are some ideas/themes/story elements that I haven't seen yet. Every single one seems quite viable, enjoyable, full of potential. And for the record, by no stretch of the imagination are they my own invention. Each can be found somewhere in undead literature already--but hardly at all elsewhere. Producers, writers, directors--take note.
- Detective turned vampire. Oh wait, you say. What about Angel or Forever Knight or Blood Ties, etc.? Haven't we seen enough of these? Actually, no. All of the above are vampires-turned-detective. What about someone who is already a detective, perhaps an FBI agent or a regular cop or some such, who becomes a vampire yet continues in his (or her) job? This has all kinds of possibilities, not least watching the newborn undead learn the truth of their existence (a fascinating process with Jessica on True Blood incidentally) and at the same time solving crimes.
- Vampire Origins. With the possible exception of the Dracula 2000 trilogy (which was fun, but made little sense since vampires predate the birth of Christ), this is a startling untapped vein (sorry, sorry) of intrigue, mystery and adventure. Consider how much Spielberg got out of the Holy Grail and the Lost Ark of the Covenant! Think also how vampires themselves might view the question. Would they be any less divided on such than mortal men?
- Undead Secret Masters. Paranoia is good wellspring of story-telling, if a sad facet of normal human existence. That is why The X-Files' frankly ridiculous theory about the JFK assassination had "legs"
- Bloodlines. Quite simply, there are different types of vampires--each has their own culture, powers, weaknesses, etc. Kindred: The Embraced dabbled in this ever so slightly, as did Forever Knight but what about exploring the idea as a genuine story element with real consequences? How would it be if some vampires burned in sunlight, while others could shapeshift and still others needed to sleep in their original graves, and so on? Imagine how such bloodlines might interact!
- Mysticism. Understandably enough, the vampires portrayed on shows like The Vampire Diaries and movies like Let Me In are grounded in the physical. But what about a totally different direction? Legends of the supernatural tell much stranger tales--of beings that can be in two places at once, that are in some sense not even matter as we know it, vampires as more akin to blood-drinking ghosts than paranormal predators of humans. Remember the owls on Twin Peaks? Or the spookiness of the Let's Scare Jessica to Death?