Rubber Flooring Mat 4' X 6', 3/4" – Extreme Training Equipment
Amazon.com: BDK All Weather Rubber Floor Mats for Car SUV & Truck - 4 Pieces Set (Front & Rear), Trimmable, Heavy Duty Protection : Automotive
Rubber-Cal "Ramp-Cleat" Non-Slip Outdoor Rubber Mats - 1/8 inches x 3 feet x 4 feet Floor Mat - Walmart.com
Costco (in Canada at least) has these sweet rubber mats that remind me of the gym. Way cheaper than Amazon since they are heavy as heck! It's flat on the other side :
Amazon.com: Motor Trend Original FlexTough Black Rubber Car Floor Mats with Cargo Liner - All Weather Automotive Floor Mats, Heavy Duty Trim to Fit Design, Odorless Floor Liners for Cars Truck Van
Club Car Floor Mats | Golf Cart Floor Mats From Xtreme Mats – XtremeMats
Rubber-Cal Diamond Plate 4 ft. x 10 ft. Black Rubber Flooring (40 sq. ft.) 03-206-W100-10 - The Home Depot