I ride 4.5 miles (~7-8 km) each way to work. I wear my normal work clothes of khackis or dress pants and a button down shirt. In the fall and winter I don't sweat a ridiculous amount. The key is to NOT dress warmly. If it's 55 degrees out I won't even wear a jacket. If it's 40 I'll wear a relatively lightweight breathable jacket with no sweater. In the summer I've been know to change my undershirt T, which is fairly moist with sweat, but I keep the outer shirt on for the work day. I also use a deodorant when I change the under T. If sweat is the main issue, as others have said, don't pedal so hard! One other tip would be bike half way to work, make a pitstop for a light breakfast, then continue on with the second half. This way you won't be nearly as sweaty when you get to work.

One last suggestion is to bike part of the way and drive the rest. Folding bikes are great for this!