DRACULA is indeed the "granddaddy" of vampire novels in the sense of
influence; the earlier works weren't anywhere near influential, and Stoker made up a
lot of the rules (or at least transmitted them from folklore).
There is a very strange book THE VAMPYRE, by a very strange man, Montague
Summers, that is an excellent compilation of vampire lore. Mind you, he BELIEVES
in it.
Vampires have the ability to shapeshift, usually into a bat, a wolf, or a
mist (which allows them to enter rooms through keyholes, under doors, usw.).
This is probably what you are referring to in AGYAR, a book I have read only once
as I didn't really enjoy it.
There are a lot of different vampire novels around these days, and even
different genres: not only the traditional horror stories, but romances and
mysteries with good-guy vampires. One rule you'll find in the new ones, but not, I
think in any traditional ones, is that a bitten person does not become a
vampire unless there is an exchange of precious bodily fluids--the bitten one has to
drink some of the vampire's blood. Another, which was pretty much latent in
the traditional stories but has been made explicit in the modern tales, is
that the bite of a vampire is not necessarily lethal and bestows intense erotic
pleasure. The modern good-guy vampires tend to sip from people they either
pick up in clubs (what DO they do about AIDS?) or keep as sort of pets. There is
a lot of confusion, especially among the less able authors of paranormal
romances, over just what applies to vampires (garlic, holy symbols) and what works
on werewolves (silver).
Some of the best current ones --- Tanya Huff's Vicki Nelson series, all with
"Blood" in the title, featuring Vicki Nelson, a medically-discharged homicide
cop turned P.I.; Mike Celluci, her former partner and still sometime lover;
and Henry Fitzroy, vampire, author of bodice-ripper romances, and natural son
of Henry VII. They are published mainly as dark fantasy but qualify equally as
detective stories.
Susan Sizemore's "Laws of the Blood" series, featuring the Hunters: the
vampire cops who keep the other vampires in line, and their human Companions.
Pretty gory, more of a romance theme, but very good, focusing a lot on vampire
ethics and politics.
Christine Feehan's "Carpathian" series are popular, as are the Anita Blake
tales by Laurell K. Hamilton, but those both seem to feature more erotica and
bloodshed than I care for so I haven't read them.
tal