I'm fortunate that I can go part way on the train. So I have a little regimen that I follow as best as schedule permits:

1. ride train to work (pretty short rides, ~5 miles), ride bike home (~25 miles) - so most of the sweat is at 7PM
2. bring all clothes for the work week to the office on Monday, so I don't need to carry them (eventually, everyone in the office has made the same "Don Draper" joke. Hmm). Bring them back on Friday or when driving near the office on the weekend.
3. Bring my (large) laptop to the office on the same schedule
4. Have enough bike shorts and jerseys so that I'm always wearing fresh ones *
5. Baby wipes & deodorant available at the office.
6. Sprinkle "Odor Eaters" powder daily in the shoes. My shoes are some oddball velcro'd Adidas's that I bought in Japan -- might be counterfeits or not even an Adidias design, but they are a sneaker/sandal sort of thing with lots of open ventilation.
7. I keep a cap around at the office, on days that the hair's really hopeless

Lots of great ideas in this thread!

* My calculations show that riding 4 days a week saves me ~$4000/year in auto-related costs. A few extra shorts don't seem that bad. Heck, that Rapha soft-shell jacket starts looking pretty cheap... (slaps self)