At least according to flavorwire.com (a pretty slick on-line magazine). I think they got most of them. New or old, they all are certainly spectacular. Enjoy pictures of 20 beautiful stations.

The first 10.
The second 10.

I agree with the traditional ones. The one in Antwerp is breathtaking, I remember standing in the middle of that and just slowly turning around, marveling at it.
I can only assume they had to a lot of work on it after the war was over, as Antwerp got the living snot knocked out of it in WW2...

I would add Cincinnati Union Terminal and the new Berlin Central station to the list.

St Louis should have bumped one of at least two of three on the list. IMHO it is the best looking in the US, inside and out.

Rossio Station in Lisbon is indeed quite unique and beautiful outside with obvious Moorish influence and it is a busy commuter station. It is quite a shock, though, as you walk through the portal because the inside has been completely gutted and is very modern as you can see from the picture. Yes, that's the same station. A Starbucks occupies the lower right corner in the front. The Hotel Avenida Palace is right next door and you can feel the trains come and go through the floor.
The trolleys in Lisbon are also great fun, as are the 'elevadores'.