I think that this really depends on where you are working and who your clients are. "Business Casual" seems to be the norm at most big corporations in the US these days.
If you are providing certain types of professional services (legal, accounting, business consulting), I believe that you should be professionally dressed when you show up for the initial client meeting. This often means wearing a suit or jacket and, for men, a tie. After you have developed the relationship, you may choose to "dress down".
There used to be an old rule of thumb called "two up" (or something like that.) The basic premise was that you were to supposed to dress at least two levels more formally than the client to whom you were calling on. I think that it never hurts to err on the side of being too conservative rather than too casual when calling on a prospective client for the first time.
How you dress is really part of your personal and professional "branding". In my case, I wear a tie about 95% of the time when working. Even though dress codes have become more casual, I have continued to dress in a more conservative fashion. In my industry, I am known as "the guy who always wears the suit" and this plays well into the image that I am trying to maintain.
I`m sure that in some industries, my conservative dress would make me look like a freak, but in my profession, it seems to work well. (Unless people really do think I`m a freak and I just haven`t found out yet ..)