Wow, great suggestions here all around. That's why I love EN World; there's no end to all the great ideas I get and there's no telling how much better it has made me as a DM, in regards to knowledge of the game
In any case, Heroes of Horror is a great book and more than worthwhile investment (it should be #1 on you list right now

), and has some great ideas in it for Horror Campaigns. Libris Mortis is a top-of-the-line book about undead, and will also greatly enhance a horror-based game (esp. if used with HoH). I don't own Lords of Madness, but it would be a runner-up for horror-based campaigns, I am sure
I'm a CS, so I have the search function, and looked up a few things for you here
Creepy.... - possibly the best thread on EN World, there are pages and pages of advice here on how to throw creepy stuff into your campaign. And a lot of it has to do with little dead girls
Game-Related Music Threads and Links - the first one is "Scary Music"; I think it'd help you
Need horror campaign idea - soem more good advice and ideas, even in the first post
What Makes A Horror Campaign Scary? - I didn't read this one through (it seems more centered on d20 Modern) but you can likely apply the info in it for D&D in general
Best system for horror... Thoughts? - This thread is a bit OT, but you might be able to glean some ideas from it, like what works in Call of Cthulu, and maybe you could try to incorperate it into D&D
So... what do you do with fairies? - this thread, while about fairies, has a lot of good suggestions to make them creepy, micheivous backstabbers, which could work
Article on Scary Monsters - this thread has a link to the MSN site about creepy monsters. Might be able to get some feel for it rubbing off on you.
Hope those help!!
cheers,
--N