Generally speaking, I get my manga from one source; Rightstuf.com. They ordinarily price their manga at 25% off, but they run fantastic sales for the holidays starting before Thanksgiving.
Prior to Thanksgiving, there were three waves of savings on all sorts of titles for manga, anime and live a tion as well. Starting 12/01/14, they have had daily sales. Every day there are about 80 items up fort pretty deep discounts.
It looks like most of the items are not newer titles, but if you are looking to back fill on manga titles are DVD/Blu Rays, now is your chance!
There a new wave every day. There will be new titles for three more days, but the items from prior days would still be discounted while supplies last.
So check it out at www.rightstuf.com!