Wow! Just wanted to add my voice to this. I agree having your fonts and clipart organized is a HUGE timesaver for the graphic designer. Should be done as soon as possible. I'm going to visit the sites mentioned. I have done a hap hazard effort in this area. It works, but not the best method.
Letting the client see it? My experience is that that has the propensity to exponentially increase the time you'll be at the counter. And, as others have already stated, you may end up making a sign with your name on it, but one that you're not entirely proud of.
When we sell RTA lettering, we have a styles chart on the wall. I've boiled our font list down to about 70 styles. Some casual, some formal, headline text, scripts, blocks, and some novelty fonts. We tell them that they can pick from that list. If they want to specify a particular font, we charge a flat rate of $10.00 to locate and load their "pet" font. That isn't much of a fee, but believe it or not, it usually discourages them and they pick a font from our list. If they in fact do want it, it gives us a little something for our time.
Just my $.02.