For a scholar looking into vampires/folklore try slogging through
Montague Sommers. Consider his stuff out of print and best found through interlibrary loan.
Historical vamps that shaped Dracula--try googling
Lord Ruthven. He was way more popular than Dracula for a loooooong time. Check folklore books by
William Baring-Gould, Sabine Baring-Gould.
For lighter reading there are whole series of vampire books in the romance sub-genre called
paranormals. The plots are girl-meets-boy, but one or the other of them (sometimes both) is some sort of paranormal beastie. The quality of writing--as in any genre--varies. Some are light comedy, others are overwrought and angsty (popular with teens) some extremely readable, others so over the top you wonder what the writer was snorting.
(As a side, the paranormal genre is a hot seller and publishers are open to new writers, but warn that they're getting tired of the same-old-same-old when it comes to vampires and werewolf tales. I was just in freakin' Wal*Mart today and spotted no less than FOUR vampire titles on the racks. None was worth buying, IMHO. The ideas were just too tired, as were the recycled love scenes. "His eager, seeking lips
captured her eager, seeking mouth..." Oi vey.)
For darker stuff you can mine the horror genre. Traditional blood-suckers abound, along with genetic (and sometimes ET alien) variations.
Then there are the in-betweens who have done something different with vampires.
Look up: (no particular order)
Fred Saberhagen's Dracula books
Chelsea Quinn Yarbro's St. Germain series (VERY historically accurate)
P.N. Elrod's got tons of titles in
four different vampire series, including a stand-alone sequel to Dracula--The Vampire Files-11 books; Jonathan Barrett, Gentleman Vampire-4 books; I, Strahd-2 books; Lord Richard, Vampire-3 books (co-written with actor Nigel Bennett who played a vampire on TV, if that's good for reseach)
Wm. Mark Simmons (Just a dang good read)
Charlaine Harris (Just READ them!) Dead Until Dark, Club Dead, etc.
Andrew Fox (Just GET them!) Fat White Vampire Blues, Bride of the Fat White Vampire
Christopher Moore Bloodsucking Fiends (which introduces one to the joys of turkey bowling when working the graveyard shift at a grocery store)
There are many others, as it is a HUGE sub-genre now, and the rules of what makes a vampire are different for each writer. Everyone has his or her own take!
<--a cool vampire writers party!