"Cold" weather gear

Plastic bags over the socks and inside the shoes can do wonders for cold toes. If you want to buy gear, Craft cold weather base layers are da bomb. Amfib from Pearl Izumi are great, but are certainly cold weather gear. Personally, the flexability of leg and arm warmers can't be understated. Glove liners are another key. Try Colotado Cyclist as they have had sales on these this week.

When it gets down that cold (and yes, that's cold), for riding you really need something to cut the wind as well as insulate. A shell over the base layer and jersey makes a huge difference, as well as shoe covers, and thicker tights with neoprene panels over the knees (I have some I got from Performance that I've worn into the 30's). Gloves... Might even want to go with lobster claw type. Helmet liner might help too.

I wear UnderArmour Cold Gear mock turtleneck tops down to the mid teens and only throw a nylon jacket on over it on the bike down to about 20.

IP or Nike fleece tights take me down to mid teens as well, with either standard spandex shorts or tri shorts under them depending on ride or run.

Toe covers and socks for 50ish to about 40 and full booties below that.

Get a Wal-Mart type helmet for cold. They're not near as airy as the more expensive ones.

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Skullcap style hat.  I love my Nike dry-fit one, it's thin enough to wear under my helmet for riding and the fleece liner really does a good job at keep the sweat off.  Keeps my ears warm too, which is key since I got frostbite on my ears in Antarctica.  I also love my UnderArmor cold gear tights, which I wear with just a pair of regular shorts over top down to 20F. Can't help too much with the rest of the biking stuff, as I am too slow to generate much wind, and do fine with a long-sleeved base layer and a Nike dry0fit running jacket (fleece lined).  I like the jacket for long sleeves that come down over my hands and have a cut-out for the thumb.  It helps seal things up when biking. 

Get both. Then if you crash in the winter or bonk it on something it's not your expensive one you bonked

Instead of a cover, use one of the swim caps from a race

In Minneapolis we use a lot of cold weather gear   I highly recommend Craft base layers.  They will wick the sweat away from your skin keeping you dry and warmer.  The layer that you have next you your skin is very important. 

Also check out the entire C9 selection at Target. It is really good quality for about half of the price of under armor.