If you have a marketing budget, spend some time attracting users with goodies. Maybe you could offer 10% off their next subscription, or a free trial to your service for 30 days. Vouchers can also attract users as you can post your voucher on one of the many voucher sites. Many local companies here in Fort Collins have been utilizing Groupon and Living Social. Both are great ways to attract lots of people to your site in a large burst. If you are one of the lucky ones to receive a Groupon or Living Social special, make sure you check with your hosting provider to see if you have enough bandwidth allocated for the amount of traffic that could potentially come to your site.