Without a doubt, the business suit is foundation of women's business attire. Choosing a pant suit or skirt suit that fits well, is the biggest piece of your professional image. But what top you wear with it can really change the look of that suit.
One of the most classic things you can wear with a suit is a basic, white blouse, with the collar folded over the lapels of the jacket. This is a timeless look that never goes out of style. It looks very sharp and professional every time you put it on. This classic white blouse is a reliable staple that goes with almost everything, and you ought to have at least a couple. For variety, get a few basic blouses in other colors too. If you have day when you feel tired of the black power suit, you can brighten things up, with a blouse in a color like red or yellow.
Then there are various tops, without collar and buttons. You can wear solid tops or tops with a print. But if the top is too casual, don't wear it with a suit. If it is the kind of top you would wear with jeans on a day off, then don't mix it in with your professional wardrobe.
People sometimes ask if they can wear camisoles with a professional suit, and yes you can. Especially if it is in a contrasting color. However, if you do, you should keep your suit jacket on the whole day. Showing shoulders does not fit with business attire. Generally, the more skin you show, the less likely people are to take you seriously in a professional situation.
A variation to the camisole is the lace top. Again, keep the jacket on the entire day, when wearing anything sleeveless. An all lace or partial lace top in a pretty color can be a great way to change the look of a pant suit. I would advice you to avoid black lace though, because it can give the impression that you are wearing lingerie.
Thin sweaters are an option for women who live in colder climates. There are many wool or cashmere sweaters that are thin enough to not make your jacket bulky. This way you can keep your suit look even if you are cold. But when you try them on in a mall, be sure to try them on with a suit jacket, so that you'll know for sure if the sweater will bulk on you or not.
Do I need to mention that you should not wear a t-shirt with a suit? No, you probably know that already.
Why don't you make a fun evening project out of laying your pant suits and skirt suits out on the bed, and then going though all the blouses, tops, and camisoles you have in your wardrobe, to see what top goes with what suit. Then write down what's missing and do some very focused shopping on the net. You end up spending less, when you have an exact shopping list.