My experience with the Impala was that - practically speaking - the trunk wasn't as big as it looked on paper. I found that once I got my two upright suitcases in there, I had a lot of space for little things but not any other suitcases, not even my upright carry-on. So if you're shopping this may still work for you and you'll probably get more use out of the little nooks and crannies that form.

Ironically enough, I found the Camry to have one of the more generous trunks in the Fullsize category. I rented one in Victoria back in 2008 when I returned home from college for the summer, and was able to fit both my uprights, a loaded hockey bag, laptop, and upright carry-on in there with room to spare. I thought for sure one of the bigger bags was going in the back seat. The Camry of that era was only 15.0 cu ft, so I guess it's not the size that matters, but the design as well.

That being said, there are still some cavernous trunks to be found. Booking Luxury could net you a Town Car with it's generous 21 cu ft, but these are becoming few and far between. A Ford Taurus would be a great option as well and there seems to be plenty of them kicking around. It's rated at just over 20 cu ft, about as much as the old Crown Vic if you can believe it. The Lincoln MKS is based on the same design as the current Taurus so it could work as well.

I would echo what another poster mentioned and consider a van or SUV if the price fits. If the Luxury category fits into your budget then I imagine you should be able to find at least a Standard SUV for about the same price or less. Something like a Grand Cherokee or Explorer would give you a decent amount of floor space with the ability to stack higher.