While not the most stylish or "cool", the high tech ballistic nylon jackets available these days have a lot to offer. I just did a coast to coast ride, and never had to take mine off due to weather, varying from 20 to 88 degrees F, and with rain, snow, and high winds thrown in for good measure. The link below is to the one I wear. Mine is in the high-viz color. There are similar jackets from other vendors available.
http://www.olympiamotosports.com/ast_mens/ast_mens.htm
Advantages:
Safety: In addition to being virtually impossible to wear through due to pavement abrasion, they have stiff and strong elbow, shoulder, and back protectors.
Weather: They are waterproof and breathable. Unlike other rain gear, you don't wind up just as wet from your own perspiration. And it keeps rain out better than any dedicated rain gear I ever tried.
Flexibility to alter with conditions: They have a removable high tech liner. It has a fair amount of warmth, but if you take it out and stow it, which takes very little space, you are left with a fairly light shell. There are vents that can be opened in the arms, chest, and back (so the air really can flow). In the opened up configuration I rode at highway speeds at 88 degrees without discomfort. The light color reflects the Sun's heat. I don't think I'd have been any cooler in a tank top. And in any of its configurations you have the most protection that you can get against road rash and impact, short of a car.
They don't give this type of equipment away. But I would have to say that, apart from the bike and a good helmet, it's the most useful single piece of gear you can have.