It's kind of the same stuff you'd wear doing any physical outdoor activity. If it's pretty darn cold -- base layer, insulating layer, shell layer. I don't buy cycling specific winter gear when I already have hiking and outdoors winter gear. It's pretty much the same stuff with a longer cut tail, a slightly closer fit, and at least 2x the price. Often the cycling gear doesn't even work as well and still costs more.
If you want to burn money, there are plenty of brands for cycling specific gear. If you also hike, you can reuse a lot of your good gear from companies like Outdoor Research, Marmot, Mountain Hardwear, etc. If you want a good layering system and want to get it dirt cheap, search ECWCS, look at the layers, and go find the gear on eBay and at surplus stores.
My idea for cold is typically a base layer and softshell jacket. If it's just stupid cold, I'll add a fleece and soft shell pants and potentially use a thicker base layer. Wrap the cycling shoes in neoprene booties, and wear wool socks. Keep your skin from being exposed with a balaclava or combination of hat and face mask and googles.
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Fällt der Pfarrer in den Mist, lacht der Bauer bis er pisst.