I'm all for the simple commute. My commute is just over 10 miles each way but doesn't require any special clothing. I've worn everything from suits to shorts and tee shirts. While I do occasionally wear poly in the winter I'm actually a cotton guy in the warmer weather. I'll often wear a cotton tee shirt on my ride into work and just carry an extra tee shirt, which I'll change into when I get there- using the original as a towel.
I shop once a year for clothes at an outlet mall and get stuff at Timberland, Gap etc that all works fine for riding to work.
For shoes I either wear a pair of comfortable slip on shoes I've bought at the Timberland outlet store or, more frequently, my new Keen cycling shoes, which I love
- I just did a 4 day tour with them and they were just as comfy walking around on Cape Cod and on the ferry as any non-cycling shoe I might have brought.
One thing that makes it work is the Campus Pedal I use from Performance. Having a pedal that can take either a cleated shoe or a regular shoe makes it work for me. As does an upright barred hybrid "go anywhere" bike with nine speeds, a front rack, a rear rack and I love my milkcrate- throw and go- like a pick up truck!