This has to be the best restaurant in Madison! A very relaxed open atmosphere in the Machinery Row loft. I love the look of the space - exposed beams and ductwork, gorgeous tile and pewter bar. I also really like the flip out windows at the kitchen - you can look in and see what is going on.
Checkout this article for why it made the Best Eats 2006 at the Isthmus newspaper.
http://www.isthmus.com/eats/article.php?article=5178
The food is out of this world - french bistro. Don't miss the warm duck confit salad, skate wing, and steak w/ frites. All are delicious. I have not had a bad dish there yet. The prices are very reasonable for someone used to Chicago restaurant pricing.
Newly opened, the place is very popular. In fact, at one visit we had a 5pm reservation (due to an event that evening) and at 4:45, there were about 10 people waiting to get in!
If you like Sardine, you should also check out their breakfast & lunch place, Marigold Kitchen, which is right off the square.