Yup, I always look for the clearance sales to buy big pots, as they can be SO expensive otherwise.
I've done well at places like Target and Wal-Mart (although I rarely shop at WM, it is next door to our Home Depot) and Big Lots. Our Target store no longer has a nursery, but they do have pots in the patio section indoors, and as Mary suggested, this is a great time of year to find clearance prices on patio stuff.
Garage sales, second hand stores and the Re-Store (Habitat for Humanity) can be another great source. Hit or miss, though.
