I'm starting my third year with an Endura Gridlock jacket. Mine is hi-viz, but it also comes in blue, gray, and red.

Like all cycling-specific jackets, I like the cut--gorilla length sleeves for in the drops, a long tail to cover my butt, and no loose flapping sides. It's also water-resistant, fairly breathable, and has good venting. I can wear it with one long-sleeved wicking t-shirt underneath from 55 down to 30 before adding a second layer or switching to a heavier layer.

Best of all, it's pretty cheap. $99 MSRP, less online.