Be and Have Plenty
No-cost and low-cost resources for entrepreneurs and businesses.
Customer Relationship Management (CRM)
According to Wikipedia, "Customer Relationship Management (CRM) consists of the processes a company uses to track and organize its contacts with its current and prospective customers. CRM software is used to support these processes... Typical CRM goals are to improve services provided to customers, and to use customer contact information for targeted marketing."

There are several excellent commercial CRM programs on the market. Depending on the size of your customer list and your plans for using a CRM program, they may have more features than you need and a higher price tag than you want. So here are some comparable alternatives with lower costs:

Highrise helps you keep track of your customer communications and tasks. The free plan allows up to 2 users and 250 contacts but provides nothing else. Paid plans with more features and functionality start at $24/month.

Microsoft® Office Live Small Business gives you a free CRM contact manager and much more when you sign up for a free account.

Open Contacts is a free address book with CRM functions.

SugarCRM is robust and free CRM software for customer service, sales, and other staff members to use for client communications.

Zoho CRM is an online CRM system with inventory management integration. Free for 3 users or $12/month for 4+ users, which includes more features.

To learn more about CRM, check out these books at Amazon.