Now that it seems harder than ever to get an upgrade, I've started checking SeatGuru.com when I book flights online. It's a bit of a pain to toggle back and forth between SeatGuru and the reservation sites, but worth the trouble if it's a long flight, or you're a control freak, or both. This free site gives you the skinny on the best seats on the plane, broken down by carrier and airplane model (configurations differ by airline). Even if you can't book the seat you want online, you'll be armed with the good row and seat numbers when you bargain at the gate.