There is a $3 off coupon from some Chex package that some CAG posted a month ago. It is a YMMV since the original coupon is a plastic foil thing but some cashier wouldn't know or care.
Since I still can't figure out how to attach pdf documents (there's no option for attachments), I'll just refer you to slickdeals. Do a search for "best buy coupon" and you'll come up with plenty.