I have good news for you, E: your solution is quite simple. For people who work in an office every day (like myself), the work wardrobe is extensive, by necessity. For you, and those of your contemporaries who are lucky enough to work at home, you have it much easier. What I would suggest is getting two good base suits, of whatever style you prefer. Get one in black, the universal power suit color, and another in a fun color or style. This way you'll be able to have one safety suit and one creative suit, so you can portray either image to your clients. I'll warn you, this is going to be a pretty significant investment, but don't scrimp to save a few pennies. These suits can last you for years and years, and part of professionalism is being well-put together. As a matter of personal taste I prefer a woman in a skirt suit instead of pants, so I put up this little number from Banana Republic. Get it tailored so it fits nice, slap on a nice pair of shoes and a pretty shirt and you're ready to go. I would also suggest pantyhose - bare legs are unprofessional. Now, you'll get bored wearing the same thing all the time, so invest in some shirts that you can put under the suit to change things up a bit. Also, if you want to expand your work wardrobe instantly, get a nice pair of tailored pants that will go with that blazer, and you've instantly got a new suit.
So men, your mission is similar. The Banana also has some great men's suits, and I would again recommend a black suit for a start, and then another suit, like brown or blue, for variety. Stock up on some standard-issue button downs in a few non-offensive colors, and a couple of ties, and you've got a whole mix-n-match thing going on - you won't have to wear the exact same thing for a plethora of meetings. The key is always being able to interchange your pieces. If you have a shirt or pants that only go with one other thing, you won't wear that article very often. For people who don't want to drop hundreds on a work wardrobe, you want flexibility. The suit at right is very smart. Don't forget to tuck in your shirt, and for the love of fashion, please get a few pairs of black dress socks to wear with your good shoes. The last thing you want is to sit down for a meeting and your old, holey, white, knee-length socks are sticking out. Then it just looks like you're playing dress-up.
To complete the professional look, there are a few little extras you can add that will really seal the deal. Girls, you can wear your hair down as long as you keep it looking neat and orderly at all times. If not, you might go for a simple bun, or even a French twist. Guys, a little cologne wouldn't hurt, and the ladies can do the same. Much to my dismay, many companies are now banning perfume and the like in the workplace because there are sensitive noses that get sick when greasy Larry in accounting walks by and his cologne is stronger than a Turkish weightlifter. Larry has ruined it for many, but a subtle scent is a nice touch, if you're allowed. Also, get yourself a respectable method of carrying around your papers. A big purse is perfect for the ladies, but guys won't do this, and I don't blame them. A briefcase is nice, but an attache case is just as good and not nearly as stuffy. The bag at left is also from the Banana, and is more versatile than a regular briefcase. I would also suggest a good planner, whether it be digital or paper, because there is a rule in business that is unbreakable. No matter how good you look, smell or work, you can't represent if you're late. Then you just look like a fool.