Remember that good consultants aren't always geographically bound; they'll travel, and frequently they can work by modem.
The best referral system is word of mouth. Ask local executives whom they have used. You've probably found a good consultant if he or she is so busy it's hard to schedule a first meeting. Trade associations also can be useful in recommending consultants experienced in your industry. That's a big advantage because you won't have to train them on business-specific issues.
Don't assume consultants are good just because they've been in business awhile. A bad one can screw up one job after another and make a living at that.
It goes without saying that you should always check references carefully. If you're searching for technical know-how, don't just call on the consultant's former customers. If possible, visit them to inspect his or her "work product," especially how it performs for nontechnical users. It's important to look at the solutions the consultant has installed. If they almost always use the same hardware or software, chances are, you're dealing with a value-added reseller (VAR), not an independent consultant. VARs aren't necessarily bad, but they profit by selling specific products, which might not be optimum or the most economical for your needs.
When interviewing consultants, pretend you're hiring an employee. You probably cannot judge the person's level of expertise, but you know a jerk when you see one. People skills matter because consultants deal with you and your staff as they learn how the company works so they can customize the system. You don't want a condescending, lingo-spouting chiphead who will alienate everybody in sight. Get a normal communicator, to whom you might say, "How 'bout them Cubs?"
Ask about professional affiliations. Membership in the Independent Computer Consultants Association, for example, means the individual subscribes to a code of ethics. It also indicates a dedication to professional development. Then call those groups to verify that the person is in good standing.