WordPress shopping cart that supports 2 tier product variation options

The e-commerce plugin Shopp for WordPress seems to allow 2-tier product variation options. It used to be a bit buggy in the 2-tier product variation department, but I think that they’ve fixed those issues with the plugin now.

Keep in mind that Shopp isn’t free, but in my opinion it’s worth every dollar. MarketPress is supposedly going to support this as well, but WPMU Dev might take a while to release a new version of it.