it depends on the distance. in order of how frequently i wear:

1) almost always were a short-sleeve cycling jersey - summer or winter -- change my shirt when i get to work or if going into a store only if i'm significantly sweaty
2) if my commute is more than a few minutes i wear cycling shoes
3) if the weather is OK (dry) and my commute is less than about 30 minutes or so i sometimes wear jeans but most of the time cycling shorts and in winter with tights -- for my current 10-11km commute probably 80% of the time wear shorts/tights and occaisonally wear jeans when it's not too hot or too cold and dry (so i don't sweat too bad or get wet/dirty) --- as Andy said, my tights are actually running tights and i also wear other running clothes sometimes but they function just about as well.
4) for rainy weather, really hot weather or longer rides, i wear all cycling gear and completely change at my destination including underwear and socks (change my shoes outside and the clothes in the restroom at work)

i have all kinds of long-sleeve jersey of various weights. windproof jackets and vests, thin running tights, leg-warmers, thick windproof fleece tights and gore-tex pants, etc. plus about 6 or 7 different choices for gloves. over the years with all my sports (biking, running, skiing, mountaineering, etc) i have a ton of performance athletic clothing. i wear a different combo almost every day/week depending on weather.