Frankenstein Makes a Sandwich is another great one - very clever with fantastic pictures:
In a Dark, Dark Room might be too dark for really young ones, but 1st Brother really liked it starting around age 4:

I had to buy Ghosts in the House after Pepper recommended it:

The Hallo-Wiener is hilarious:

Although it's not technically a Halloween book, The Charles Addams Mother Goose has that feel because of its awesome illustrations:

The Scary Stories to Tell in the Dark boxed set is waiting patiently for when the boys are a little older - I loved these growing up.
