The best gas can I've found is the NATO style jerry can and spout that's supplied with a Swiss-Army Pinzgauer. They were outlawed by the latest DOT rules. You can still find these cans on ebay, but with a smaller diameter spout. The Swiss spout is over 1" diameter, and it'll empty the can in a wink.
The ebay NATO cans are green, but that can be cured.
