Try sidestep.com.
I have used them several times in the last couple of years instead of nwa.com and they are usually cheaper than nwa.com.
I try to fly NW for two reasons: 1) they are in my backyard and 2) as a former employee I still know plenty of employees at NW who will op-up me if there is room up front.
Last Monday I booked 3 tickets to BRU leaving end of September and returning middle of October for $537 all in on sidestep.com when nwa.com was $630 plus taxes for the same travel dates.

Edited to add: Sometimes the carrier listed will show "major carrier".
Just click on it to see who the airline is.