Blastwave FX has a huge collection of high-quality, royalty-free scary sound effects for frightening, well, anyone you want. Scare the trick-or-treaters, co-workers, family members, and party-goers with these awesome sounds.
See below links to check out and download any of the 9 Horror Sound Effects Download Packs ($25 each).
Or get a 199-sound Horror Sounds library. That one comes on a flash drive since that amount of high-quality audio would be too much to download, so be sure to order this one early!