For me, it's the Child's Play movies. The idea of a killer doll pretending to be just a doll is too good. I think Bride of Chucky is my favorite of the bunch because it's quite funny. But the first one is genuinely scary, so it's a bit of a toss up. 
Some other good ones:
1. The Descent
2. Thirteen Ghosts
3. Freddy vs. Jason
4. Texas Chainsaw Massacre (original)
5. The Thing (original)
6. The Fly
7. The Others (psychological horror)
8. The Sixth Sense
9. Jason X (my fav Jason film)
10. Ghost (a tragic love story that's also scary)
11. Event Horizon (cult classic)
12. The Adam's Family (1991)

Some other good ones:
1. The Descent
2. Thirteen Ghosts
3. Freddy vs. Jason
4. Texas Chainsaw Massacre (original)
5. The Thing (original)
6. The Fly
7. The Others (psychological horror)
8. The Sixth Sense
9. Jason X (my fav Jason film)
10. Ghost (a tragic love story that's also scary)
11. Event Horizon (cult classic)
12. The Adam's Family (1991)
