Weathertech mats rarely are on sale and they are usually excluded from coupons at most retailers.
NAPA currently (5/12 and 5/13) has a sitewide 20% off sale for rewards members (free signup) and it works on Weathertech products.
Even better, you can get an additional 10% off if you are AAA member (both % discounts are calculated off the original price which is nice). If your item is less than $100 you can use coupon code NAPATEXT for $10 off $40 that stacks with the sitewide 20% discount but doesn't stack with the AAA discount.
Even better, when you sign up for their rewards program, you get an initial $5 rewards credit that applies on top of the sale and coupon/AAA discount. Make sure you sign up before you place the order. If you sign up as part of the order process, the $5 reward doesn't get applied to this order.
A mat that is listed for $84.95 comes down to $52.96 before tax!
Note that the list price at weathertech.com is $69.95 but they charge $15 shipping. Pretty much all retailers that sell weathertech charge either for shipping or add $15 to the price.
Of course, this deal could be used with other items as well. I'm not sure what the restrictions are. I'm posting it for weathertech since it is usually difficult to get a discount for this brand.
EDIT: YMMV - apparently some floor mats don't qualify for some of the discounts. It's worth a shot though. I tried some random ones and some worked and some didn't. Some allowed the napatext coupon but not the 20% off. Some didn't allow any discount and some allowed all.