For truly shocking (not checked if they're availble as ebooks) anything by Jack Ketchum or Joe R Lansdale - I'd particularly recommend Ketchum's
The Girl Next Door and Lansdale's Short Story collection
On the Far Side of the Cadillac Desert with Dead Folks.
Again, not available in ebook, but the best Vampire novel written since Salem's Lot - John Ajvide Lindqvist's -
Let the Right One In - is worth getting hold of.
I see you have a Kindle 2, so here's a few:
Dan Simmons's
Brood (looks great, and he's a good writer) -
http://www.amazon.com/Drood-A-Novel/...=pd_sim_kinc_3
Richard Matheson's
Hell House - (anything by Matheson is worth reading)
http://www.amazon.com/Hell-House-ebo...2781850&sr=1-2
Loads of Richard Laymon here
http://www.amazon.com/s/ref=nb_ss_ki...laymon&x=0&y=0, I'd go for
In the Dark as it's the first Laymon novel I read.