Keep an eye on this thread at slick deals
they have a all the current harbor freight e-coupons. HF runs the 20% off any item three days out of every seven or so.
BTW, I've signed up for their email list a few time but never get an email, I hear it happens a lot that even if you sign up you don't get them so I just chack that thread at slick deal every few days.
Edit: Oh, and the ones that say bonus coupons, when you click "print this coupon" a second (sometimes related) coupon will also show up.