I commute on a regular basis. I had an epiphany last year and ditched all my bicycle-specific clothing. I now commute only in "regular" clothes, or, at the least, clothing that is multi-purpose. What you need though, really depends on where you live. I'm in New England, so we may have different definitions of cold.

That said, two things are your friends: 1) layering, and 2) merino wool.

Down to about 38 degrees F, I find I can get away just wearing either my Showers Pass Portland jacket (bicycle jacket, yes, but looks like a regular jacket so you can wear it anywhere) or my Columbia Wax Cotton jacket. I also own some Brooks Brother merino wool polos and some Sir Pendleton merino button-downs that help insulate down to the lower end of this spectrum.

Between 30 and 40, I switch to an Ibex Europa with a Columbia windproof shell with pit-zips.

Below 30 doesn't change the jacket, but I add Under Armour tights under the pants and switch to Patagonia Das Boots.

None of those things are exactly cheap, retail, but bargains can be had on the 'Bay. For example, I just bought a B/B merino polo for $12, shipped. I paid $100 for the Ibex Europa as opposed to $295 retail. The Showers Pass jacket was last year's model for half-price (no returns). Look for deals, they're out there.

And definitely read Grant Peterson's "Just Ride."