I personally like Ajaxparkingrus. You can print a coupon on their website.

I tried the new Wally Park, and they charged me an extra day. Drop off @ noon on Sat, pick up at noon on Tues is 3 days, but they charge 4. This was using their reservation system, so maybe they iron it out when you actually pay, I dont know. I dont care to go through the hassle of finding out.