The most important thing when you are figuring out what to wear is to evaluate the climate in which you will be riding. For the sake of touching all areas, lets consider 4 seasons.
Summer: The most important thing is to stay cool in the summer. There are many options, but something I like to do is a spandex bike short like our gel touring under a Multi-Sport Knicker. This gives the padding needed to be comfortable but an outer look of a nice stylish "normal looking" short. The multi-sport short and knickers are nice because the garment stretches and moves with you as you cycle. For a shirt, if a short sleeve cycling jersey isn't the look you're going for, then maybe a Rowdy Jersey will give the appearance you might be going for. Add a set of DZR cycling shoes, a pair of wigwam socks, and a pair of sunglasses and you're all set to go. Don't forget the sunscreen!
What to do if it rains: Have a nice waterproof cycling jacket on hand. A waterproof jacket like the O2 Raingear and matching rain pants will keep you dry, and they won't take up much room in your bag. A set of wheel fenders will help keep the water from splashing you.
Spring/Fall: The spring and fall can be a tricky time to dress properly for commuting. The problem is that in the mornings it's very chilly but then it will warm up to summertime temperatures. When you experience a 40 degree temp swing in a day, how do you prepare for that? Well, base layers are a great place to start. These are available in several fabric weights. A polyester/fleece base layer will help keep the heat in more than a nylon/lycra base layer. Another great option is leg warmers and arm warmers. These will keep your legs and arms warm, but are easily removed for when the temperature rises. Another good idea is a cycling jacket. These come in many different styles and options. Look for a high quality windproof and waterproof jacket. These are great to have if you get caught out in a chilly rain storm. Also, they can be stuffed into a pouch for easy storage. Last, don't forget the tights. A pair of spandex tights will keep you comfortable as you move into late fall or early spring. Other great accessories to include are a pair of shoe covers, a thin pair of gloves, and a waterproof helmet cover.
Winter: Winter riding is really where you need to gear up. As the conditions get worse, add layers. You can always take a layer off if you over heat. In addition to the layers mentioned above for the fall and spring, you may want to consider a heavy duty shoe cover. These will really help keep your toes warm and comfortable. Same goes with your hands. A nice pair of full finger gloves made of windproof materials will be necessary. For your legs, it's time for a pair of Roubaix tights or bib tights. Roubaix is a rugged and stretchy material that will keep you especially warm in the cold weather. The key to winter riding is staying dry, so always keep a good waterproof jacket and wind pants on hand.