Unfortunately the glorious days of 1400x1050 4:3 laptop monitors are long behind us, and most laptops seem to be running at 1280x800.
You know, obviously this depends on your requirements, but as a portable computer, I think a 13" screen is actually pretty good over something larger. It decreases the width of the computer, and makes it easier to transport and use on the go. If you need a desktop replacement, well, I guess 13" isn't for you.
I myself have my PC at home, with my 22" and 15" monitors attached, and a 12.1" laptop for mobile computing. I haven't found myself wanting yet.
Also, you could buy a larger monitor, and have the laptop output to that when you're at home or the office/whatever.