Trails.com
What To Look For
The best quality rain jackets should not only keep you dry but also let you breathe. A rain jacket of quality construction is made from a breathable but waterproof fabric that lasts a long time, has pit zips for ventilation, sealed zippers and zipper garages, reinforced seams, a hood that can adjust and fit a helmet if you are a climber or skier, and long enough fit in the torso. Top brands are Arc'teryx, Patagonia and Marmot, though there are many others that make a quality jacket for a slightly less price. Many companies, such as Arc'teryx, use trusted materials such as Gore-Tex Pro Shell, but some, such as Patagonia, have developed their own. Their waterproof shells are constructed of H2No material, which is not only effective but recyclable through their Common Threads recycling program. Buy a jacket that guarantees to keep you dry and if it doesn't, send it back.
Common Pitfalls
If you live in a rainy region or will be traveling in one, it's worth shelling out a few more bucks on a jacket such as the Alpha SV or Theta AR from Arc'teryx. Several companies have lifetime guarantees, and if your zipper goes kaput after average use they will repair it for you. Look for a jacket that is your preferred weight as well. If you rarely see rain and only want a lightweight "just in case" jacket then the heavy duty ones aren't for you and on the opposite side of the spectrum, if you plan on being in heavy rain a lot don't get one made of PacLite material.
Where To Buy
Buy your rain jacket from an outdoor store that consistently stocks top of the line rain jackets such as Arc'Teryx or Patagonia. Try on jackets at these stores, and then shop online for a possible sale. The biggest mistake when shopping for rain jackets is that people don't try them on. A good one is pricey, so make sure you that you love it and are comfortable with wearing it for the next several years. Sometimes eBay stores sell great rain shells, but make sure that they come with the tags if you are buying them new.
Cost
A good rain jacket can cost anywhere from $150 to $600. It all depends on what particular model and brand and what time of the year you buy it. In some rainy regions, such as southeast Alaska, local shops aren't going to put anything on sale because rain gear consistently sells, but in other areas, shop for rain shells during early spring or end of summer sales when they may need to make room for a shipment of rain jackets in a new style.