Updated Saturday to reflect changes.
No end time given but presumably ending some time Monday:
TapOut has 50% off a lot of stuff for what is termed a Black Friday sale but still going on as of noon EST on Saturday.
UFC Store has plenty of nice discounts in what is now called a extended Black Friday sale.
Saturday through Monday morning:
Updated: Ring of Honor's store has 40% off all DVDs and apparel through Monday morning at 9 AM EST.
Friday through Monday night:
WWE Shop has 20% off everything (as well as a "doorbusters" section), free shipping within the US, and $5 flat rate shipping internationally.
Wrestling toy vendor Ringside Collectibles has a sliding scale of discount codes as well as an array of discounted items, as well as a free Mattel WWE Legends Series 4 poster for orders over $75.
Dragon Gate USA is offering a 30% discount off all DVDs, shirts, and hats.
Presumably for the next month:
Highspots has a "Christmas Sale" (keep your eye on the listings on the left sidebar) consisting of stocking stuffers starting at 99 cents, wrestling action figure grab bags, a shoot interview DVD grab bag, a wrestling book grab bag, and more. The clearance section is also worth looking at, especially as it includes a great deal on Classic Memphis Wrestling DVDs: 3 for $12.25.
Not a sale, but I have to recommend them:
Smart Mark Video's second sampler DVD is available for $1.99 and they're also the sellers of the J.C. Bailey tribute set, which includes 2 tribute shows and a DVD of some of his CZW matches. All proceeds on the set go to his parents to help pay for funeral expenses.
Jim Cornette's stuff at Cornette's Collectibles is pretty awesome, especially his DVDs and the Midnight Express 25th Anniversary Scrapbook. He also has plenty of old magazines and programs in excellent condition.
Feel free to suggest other sites in the comments. I didn't want to include sites that I wasn't familiar with as I don't want to steer anyone the wrong way.