Starting with the peripherals, Steelseries is running a Cyber Monday sale which includes some WoW mice and mouse pads at up to 40% off. They also come with a free set of touchscreen controls for your tablet and free shipping. You'll also find some headsets and other accessories on sale at Steelseries. Once you make the move to a mechanical keyboard, there's no going back. Newegg has one on sale for $49.99 after rebate. They also have a 27" IPS monitor half price at $199.99.
PC hardware deals
I believe that the single greatest upgrade you can make for your PC's overall performance is to get a SSD (solid state drive). Even a small sized one will be enough to hold your Windows installation, some applications, and a few games including WoW. Games will load quicker, and your entire PC experience is smoother and more responsive. Amazon.com has a large list of SSDs on sale, as does Newegg.com. A good rule of thumb for SSDs is that anything 60 cents per GB or below is a pretty good deal, but you will obviously pay quite a bit more for performance brands.
WoW doesn't need the best GPU in the world to run at a decent frame rate, but if you're stepping up to a new 2560x1440 resolution monitor, or want to turn on some extra bells and whistles such as anti-aliasing and ambient occlusion, you will need a pretty decent video card. Something such as this Radeon 7870 for $139.99 AR, or this GTX 660 for $169.99 AR will handle WoW like a champ at almost any setting. Once you reach that GPU threshold, WoW is really more of a CPU bound game when it comes to performance. Newegg has almost all of the Intel processors on sale. The Core-i5 processors such as the 3570k or 4670k are the best bang for the buck for gaming. Stepping up to something like a i7-4770k won't improve gaming performance that much, but it will help with multi-threaded applications and heavy multi-tasking.
Laptops and pre-built PCs
If you want to go the pre-built route for your desktop, and have a lot of money to spend, Alienware is running a sale on their desktops and laptops today. For a good deal on a high end gaming laptop, you can get the MSI GS70 which comes with free 50" HDTV. For something a little more affordable in the gaming laptop realm, there is the Lenovo Y510p for $799.99 with the listed promo code.
If you're searching for a WoW-related gift, you can get the mammoth hardcover edition of The Art of Blizzard Entertainment for $40, or the World of Warcraft: Ultimate Visual Guide for $14 today only if you use the coupon code BOOKDEAL at checkout.