Even if you're a small boutique retail business, use creative ways to gather the information. A drawing for a gift certificate or other item is a wonderful way to get it. If you your customers are engaged in a questionaire you should take full advantage to get additional information you have always wanted to ask.
It's important to know exactly where your customers live, work, lifestyle, etc. The more information you know about your customers, the easier it is to communicate with them.
The basic information you want is:
With this little bit of information, you will immediately know where most of your customers live, be able to do a direct mailing to them. You will be able to call specific customers when new product arrives. And finally an email marketing campaign with photos and a special offer that will remind them why they love doing business with you.
Sure you can purchase lists. But the lists are not your customers. Having your customers information is more like having the true essence of your business. That is a concentrated list of people that already trust your business. People like to use a business they trust.