The Standard: Full-coverage waterproof/breathable jackets weigh as little as 10 ounces these days, which is great news for backpackers. Unless you're hiking in extremely wet environments–where you want all the bells and whistles–your should look for the lightest, most breathable jacket you can afford. It will sit in your pack 90% of the time, which makes anything heavier illogical. But when it does rain, you don't want to soak in your own sweat. For that reason, a breathable fabric and pit zips are essential. Other wants: a hood that turns with your head, a decent brim that doesn't drip on your nose, and pockets that don't fall under your hipbelt.
Variables: There are numerous waterproof/breathable membranes and coatings on the market–many of them indistinguishable except in the lab. As a general rule, the more you pay, the more breathable the fabric. Two standouts are Gore-Tex and eVent, with the latter getting a slight nod in recent BACKPACKER field-testing.
Take The Chance? BACKPACKER editors constantly argue whether it's worth carrying raingear in places with infrequent precipitation–like the Sierra in summer. Do you really need protection from the 10 minutes of rain you might get some afternoons? The editor who wrote this buying guide says no–you're better off with a few extra Snickers bars and ducking into your tent if a real storm rolls in. Disagree? At least cut back to something that weighs 12 ounces or less.