If you're riding for very long, though, you will probably want padded shorts. I used to think they were silly, but after a couple of rides where my butt was seriously sore afterwards and one where my junk went numb, I swapped out my old saddle for one with a split down the middle and started wearing padded shorts and now I can bike for 40+ miles without getting sore.
I like my cycling tunic/jersey thing because it gets really good airflow, but I've gone on long rides in just a plain old t-shirt, too.
(I do look at a lot of bikes.)