If you dislike the new unvented or "self vented" gas cans, here is an idea from one of my hunting buddies.
Go to an auto parts store and get a short tire valve stem and remove the valve core. Carefully drill a 3/4" hole (with a hand drill, making no sparks!) where the vent should be (behind the top handle hole). Push a stiff wire from the new hole and out the fill/spout hole. Put the valve stem on the wire and secure with a bend in the wire. Pull the stem out and snap it into the 3/4" hole. Screw on the cap and you now have a vented gas can!
PS- BE AWARE OF GAS VAPORS, THIS PROCESS CAN BE DANGEROUS!!!!