Eurostar's the obvious one, but I've seen scanners at Gare du Nord for TGV/Thalys as well, and when we caught TGV from Barcelona Sants to Paris (Gare de Lyon, I think) we got marshalled into some sort of departure lounge at Sants. Only time I've ever seen that in Europe though. Oh and changing from Eurostar to ICE in Brussels we had our ID's checked before being able to get to the platform (this was on the 23rd of December though).