lightweight windproof jacket
Sportful's Hot Pack Ultralight is an incredibly light jacket, just 50g, that is fully windproof and water resistant. It can be rolled up into it's own integrated bag and will disappear inside a jersey pocket. With jackets like this we're running out of excuses to cancel the ride when the weather is looking iffy.
The Turbulence jacket from dhb (the in-house brand from on-line superstore Wiggle) is a lightweight windproof top that's an ideal outer layer for cycling on cold days, and it easily packs down small enough to stuff in your back pocket if the weather should turn balmy while you're out on your bike.
The Rapha Wind Jacket (formerly the Stowaway Jacket) is made from a windproof, water resistant and extremely breathable 100% Nylon fabric, the cut of its jib is classic cycling with a long-cut back for a better fit on the bike and a dropped tail too, the sleeves are tailored and long enough to be stretched in the drops without wrist-gap creeping in.