This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
When you commute by bike to work, you'd probably like to have clean
clothes that don't look like they've been at the bottom of your closet
for a couple of years. Here are some suggestions for achieving this
Take a week's worth of clothes to work ahead of time and leave them
there. You'll probably have to do this in a (gasp!) car. This
means that you'll need room in your office for the clothes.
Carefully pack your clothes in a backpack/pannier and take them to
work each day. It has been suggested that rolling your clothes
rather than folding them, with the least-likely to wrinkle on the
inside. This method may not work too well for the suit-and-tie
crowd, but then I wouldn't know about that. :-)
I use the second method, and I leave a pair of tennis shoes at work so
I don't have to carry them in. This leaves room in my backpack for
a sweatshirt in case it's a cool day.