Don't forget about Halo Evolutions! That book is great. It's is a bunch of short stories taking place at various times in the Human/Covenant war, and it is really great!
And there are 6 more books coming out, not counting the remakes of The Flood and First Strike. There is a Forerunner trilogy coming out, written by Greg Bear, and three new books by Karen Traviss. So with the exception of the remakes, I will be buying them all!