I've eaten at Cafe des Architectes several times and have always been immensely impressed; those are the best dinners I've had at a contemporary American restaurant within the city limits in recent years, excluding super-expensive restaurants like Alinea. I've loved Chef Noguier's cooking at his various restaurants. And the room is very spacious and pleasant, part of the curved glass facade of the ultramodern Sofitel. It's also noteworthy for its relatively low prices, with their three-course prix fixe menu for $45 every night, and their three-course "neighborhood friends menu" for $32 Sundays through Tuesdays. Maybe that's not a concern for an expense account dinner, but it's great when I'm paying my way.
Those who have enjoyed dining at Atwood Cafe in the Loop in the past will be happy to hear that Sable has Chef Heather Terhune running the place, which is why she left Atwood.
Beware, the Purple Pig does not accept reservations and I've heard reports of lengthy waiting times for a table, even on weekdays. That would be a dealbreaker for a business dinner.