I've found Railriders' Weather Pants to be excellent for three-season backpacking. They're tough and comfortable.
Weather Pants listed at Railriders website are in a flat front version, rather than the pleated front version that has apparently been discontinued. Too bad, since I don't like the flat version nearly as much as the pleated ones. Nevertheless, so far at least, I believe the flat front version is still a very good hiking pant -- just not as comfortable as the old pleated version.
As for cold and windy conditions, the Weather pants plus Ibex woolie bottoms & GoLite Whims (or Reeds) are right up there with the cat's pajamas.
I recently purchased the winter version of the Weather Pants, but haven't put them to use yet. With additional ply as described by Railriders, the Winter Weather pants appear to have only a bit more "body structure" than the regular version although they weigh a few ounces more. (For some reason, considering the extra material for the pleat, my old pleated version of the Weather pants weighs a few ounces less than the current flat-front style.)
Note: Railriders' winter sale at railriders.com is now underway, with price reductions for certain sizes/colors of Weather Pants (both regular and winters versions) & Extreme Adventure pants. The Adventure Tops and Eco-Mesh Shirts are also at reduced prices.