Check out RetailMeNot.com. You can either get coupon codes from the site, or….if you’re a Firefox user, check this out.
It adds a little extension to your browser. When you visit a shopping site, a popup bar appears telling you that there are coupon codes and lets you select one from a list. It also shows the success rate for each coupon.
I haven’t actually purchased anything using one of their coupon codes, but I get the popup at major shopping venues. Don’t know how many Canadian sites it works for, but cross-border shopping is looking pretty inexpensive to Canadians right now!