If you fly a lot, I suggest you visit SeatGuru.com. It currently only covers American, Continental, Delta, United, and US Airways. But what it does cover, it covers thoroughly.
For example, it shows the layout of the American Airlines Boeing 767 going to Hawaii and indicates which seats are “Very Good” and which seats are “Bad.” What’s particularly valuable though are the comments as you move your mouse over specific seats: “Seats 19 A,B are really bad seats, very poor legroom, reduced recline.” Now that you know, you can leave those seats for some other sucker!