Leads are the key to startup success. Keeping track of those leads is essential to your success. There are lots of applications to help you keep track of all those leads.
One of the easiest and most affordable options is MailChimp. This free online option will help you keep track of all of those potential future clients in one place. You can create a variety of custom lists based on specific clients and send email blasts from one central place.
As you build your website, include a signup form to help you collect their contact information and send a "thank you" for sharing their info.