I should think several things would work, Matt. Something made of Polartec Power Dry would make an excellent second layer over a thin base layer. REI makes a good, basic piece called the Power Dry Zip T-Neck ($38; www.rei.com). I wouldn't call it a "baggy" garment, but it's not skin-tight and is designed for layering. L.L. Bean makes a polo-style, short-sleeve shirt of the same materialthe Power Dry Piqué Polo ($36; www.llbean.com). That gives you a bit more flexibility in not-so-cold weather, plus it looks pretty good.
I think the other arena to explore is in the windproof light shell category. You could, for instance, get a Marmot Scirocco Windshirt ($80; www.marmot.com). It's a great layering piece for blustery, cool conditions, where you want some wind protection and breathability, but don't want a ton of waterproofness. Very light (ten ounces) and packable. Throw it over a base layer and you've added 15 to 20 degrees of warmth to your outfit. Patagonia's Helium Windshirt ($65; www.patagonia.com) is even lighter at six ounces, although at the expense of pockets and a full front zip.
Sometimes, even just a wind-resistant vest makes a tremendous difference. Mountain Hardwear's Windstopper Vest ($115; www.mountainhardwear.com) is just about 100 percent windproof, while still very breathable. And its light fleece material is surprisingly warm. Vests are perhaps the most useful and underrated garments around; I wear them constantly when biking, hiking, or putzing around outside on those not-so-cold days. Keep the torso warm, and the arms, legs, and head will follow.
Lead Photo: courtesy, Marmot