While looking at the O'Reilly 50% off bargain, I also found Apress had some bargains for Cyber Monday.
In some cases, $15 is less than half price. Very handy (especially for people wanting to learn a new skill as part of their New Years Resolution!)
Apress Media "Every eBook $15"
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They have such a huge range, it's hard to pick books. It's to their own detriment IMHO :-/