A B2B web site as a marketing tools first starts with a "SWAT analysis" (google it) of your customer's industry, then of your client's position in the industry.
I stress that it is important to do both these days since "everything" is in a high state of flux.
Next, looking at the customer's SWAT, you want to determine how you can add value for your customers with a web site. News? Directory? Catalog? Chat/message boards? In any case on this site you must have,somewhere,who, what, when, where, how, why and how much.Not always easy answers. Give the client a checklist with each of those points, review each answer. Also, ask for the CEO's elevator speech.
If it is a very competitive B2B market, it might be wise to have your clients take a look at some of the more aggressive B2C sites.
Are they trying to maintain their leadership status or are they trying to working into a new niche or overcome an established player?
In any case, keep in mind that your client doesn't want to get out too far in front of the their customers. If the industry standard is unsophisticated and basic, then you don't want a lot of flash or Flash. But, likewise, if it a high-tech or marketing industry, it might be wise to invest in some high-end creative. You need to clearly show what is remarkable about your client, but you're not going to change the industry's culture or style. (On these project there is usually someone--often the webmaster--who does not get that.)
But, during the entire process the business client typically is focused on their own needs and not looking clearly at the needs of their customers. And it's the needs of their customers that need to be the driver. The wise webmaster addresses BOTH, letting the needs of the client appear to rule because they are the ones paying the bills. That sounds a tad unprofessional, but that's life.