Yes, with NW, after you book, you can go back into my reservations and change your seat assignments to exit row. You cannot do this as a base member I believe but can as silver, gold or platnium.

I got my AS certs in the mail three days ago just for giggles, will never use them... I am traveling soon to Asia on NW thru MSP AND PDX eventually to SIN. Picked my exit rows out right after bookings. Pre selection of exit row seats are one reason I stay with NW...

Mykal