Worn as the final outer layer, a cycling jacket or gilet can be deployed to face off with any one of hundreds of different weather conditions. Wind, water, freezing temperatures, it's fair to say that there are as many varieties of bicycle jackets and gilets as there are riders. Bearing that in mind, let's narrow things down and provide some advice.
There are two types of rides in the rain. The first is the rain all day ride, and here some serious protection is required to combat moisture ingress. We would recommend looking at the Gore-Tex offerings from brands like 7mesh for this type of riding.
The other ride is sometimes the hardest to prepare for, and this is the intermittent rain ride. In this instance, you can either go for a packable layer that can be whipped on and off as required, or a water-resistant softshell layer which can be worn all day (this works particularly well on cooler days).
For 90% of rides, a windproof cycling jacket teamed with a base layer and/or jersey is all the protection you need, and will significantly contribute to your on the bike enjoyment. In warmer months or when teamed with other layers, a gilet is also indispensible for keeping comfortable when faced with changing conditions. By nature more breathable than their full rain protection counterparts, many windproof layers come with basic 'get me home' shower protection. Remember, always choose the product that suits your needs and be sure to check the product page carefully to see an item's detailed features.