The best thing a supplier can do for its customers (apart from providing a great product, of course) is to make them feel part of a community.
They say that getting increased business from existing customers is a lot more cost-effective than trying to generate new customers. I'm sure that's true. But I wonder if the marketing departments in most business-to-business companies are playing their part in retaining and increasing the business from existing customers? Is that job just being offloaded to the sales rep who looks after that client, or even your technical support people? Do existing customers actually get less love from your company than they did before they'd placed their first order, rather than more?
I came across a company not long ago which produced a quite impressive glossy news publication, clearly aimed at explaining its products' benefits to prospects via news stories, case studies and technical tips. It was a decent effort, published at significant effort and expense. It didn't really make that much sense to send it to existing customers (not least because it had the occasional promotion which was only aimed at new users), so once somebody came on board as a customer, the marketing department stopped sending the publication to them. That was fair enough, but what was it replaced with? The answer, you'll have guessed already, was nothing.
What if everyone does this? Imagine you're a customer of company A. After having been courted for a long time by company B and company C, you decide that the benefits which company C has been telling you about in its expensively-assembled marketing material are enough to persuade you to make the switch. Suddenly, company C's marketing department aren't interested in you any more. It's quite likely that company A's sales department will get stroppy with you and not put you back on the prospect list either, with the result that the only company left actively marketing to you is company B! And this for a genuine customer who's demonstrated they're prepared to change suppliers. It's insane.
The best thing a supplier can do for its customers (apart from providing a great product, of course) is to offer them additional services which they'd miss if they left, and to give them confidence in the company by making them feel part of a community. People like to know others are continuing to make the same choice as they have. You don't need to give them a list of all your other customers, just ensure that they know they're not alone. I've always taken the opportunity to run competitions, or send them giveaways – anything that you'd only do if there were lots of people taking part.