At least as of the evening of August 1, but I have no idea how long the books will stay that price.
If you're a fan of historical mysteries, I highly recommend Medicus. (I'd link a review, but I read these long before I got on BL and have only reviewed the fifth in the series.)
I've not yet read Grace of Kings myself, but I've enjoyed Liu's short story and am willing to take a $2 gamble on his novel.
I've not read Assassin's Apprentice either, but it's supposedly a must-read book.
I absolutely loved Pandemonium--I think it's my favourite Gregory book-- but it's surprisingly divisive with Gregory fans. Even so, it's $1.99 right now, so there's that. Here's my review.