Every business needs a web site. That´s no longer a debate. I contend, however, that every business really needs at least two web sites. You should have one to tell about your company and your services and one that focuses strictly on providing great content about some aspect of your industry. Think in terms of a site that would rank very high in search engines for important key words.
For example — A law firm would have their formal firm site SpencerFane.com but they would also launch a site called MidwestConstructionLaw.com to act as a portal of information for anyone interested in the construction business.
The key to this strategy is search engine traffic. All you need to do is think how people really search for information. The construction companies in the above example don´t search for information about the construction business by looking for a law firm. They search something like "How to get paid for mechanical liens"?? So the trick is to create a content rich site that can compete for that kind of traffic and make sure that it directs them back to your firm´s site.