The Doll Maker.
If you do, please know that I'm definitely not with you. When I went to the Alien Panic Place at Spaceworld last year (I blame my friend for dragging me and my family there), I basically kept my eyes on the ground the whole time. And I still screamed several times.
So you can imagine that I wouldn't want to be in the situation that Jacky, Cass and Ben are in. When Jacky and Ben drag a hesitant Cass to the House of Horrors, something goes wrong and their made to face their real fears - or never leave.
The scary part about this book are the fears that the children face. Those fears aren't strange fears (for example, the fear of long words, or hippopotomonstrosesquipedaliophobia). They're normal fears, such as the fear of being invisible to others, the fear of the weird old woman down the street, etc. Most kids will definitely identify with at least one of these fears.
In fact, this book is very instrospective. All three kids are forced to examine themselves, and through that, they come to know themselves better. It was an unexpected, but welcome element in the book.
And the ending. The ending may be the scariest part. Majanka is really proving her ability to write books with a (scary) twist at the end. I found this book to be much scarier than The Doll Maker.
Scarier than the first book, if you liked The Doll Maker, you should pick this up.
Disclaimer: I got this book free as part of Enchanted blog tours in exchange for a free and honest review.
ETA: Read my review of the third book House of Horrors here.