With 38-42 degrees the biggest challenge is keeping yourself warm during the start of your commute while not overheating later on. An important part of this is getting out in the transitional temperatures now. When it's been 70-80 degrees for a while 50 degrees feels very cold. If you ride through the winter, you'll find that 50 degrees feels pretty warm in early spring. You just need to let your body adapt.

I have a bunch of fleece lined bib knickers that get me through the winter. I wear gym shorts over them so I don't go all Polish cycling team on my coworkers (only do a Google image search on "Polish cycling team" if you're resilient with regard to disturbing images). The fleece knickers are enough to keep my legs warm in anything above freezing temps, regardless of rain.

A good rain jacket is an important investment. Anything that retails for less than $100 is likely to be about as water resistant as a paper bag. Arm pit zippers are nice to avoid building up too much heat, but with my current jacket (Sugoi Zap) I've sacrificed temperature control for visibility. Under the jacket I usually just wear a "wicking" polyester T-shirt. When the temps get much below 40 I'll add a thermal undershirt. In all cases avoid cotton.

I wear thick wool socks through the winter. They feel great even when soaked. I haven't found anything that will keep my feet dry in a solid downpour. Shoe covers keep the road grit off my shoes and will repel enough water in a light rain. They also add a bit of warmth. I keep old newspapers in a drawer by my desk to dry my shoes during the work day.

I like head bands for keeping my ears warm. Something thin is usually sufficient. Mostly it's about protecting your ears from the wind. Growing a beard really helps with facial warmth.

Gloves are the real trick for me. I'm constantly on the search for the right balance of dexterity and warmth. I've got a big pile of gloves that I choose from based on expected temps. Down to about 45 degrees Fox Sidewinders are great (though they soak up water). When it's near freezing I like a pair of wool glove liners and loose fitting ski gloves. Between 35 and 45 I'll use Seirus All Weather gloves. You can usually get them cheap at REI garage sales because people have unrealistic expectations about how warm and water proof they'll be.

If you find yourself getting really cold, try a helmet cover -- even when it isn't raining. Those things are like wearing a space heater on your head. They don't keep your head dry because you sweat like crazy, but they will keep you warm.