Michael Cage offers seven great Low-Cost, High-Impact Marketing Tools.  Here are my favorites:

#4. Call your clients. Yes, call them. On the phone. In today’s rushed and hectic world, a little human attention goes a long way. If you want to turn spare minutes productive, keep a list of clients who bought from you in the last 30-90 days nearby. When you have free moments, call and ask how the solution you sold them is working. Aside from generating enormous good will (”they actually care about me!”) … some will have new needs or questions that will lead to new sales.

#7. Ask everyone for referrals. People who buy from you? Ask for referrals. People who don’t buy from you? Ask for referrals. Here’s a simple, no-cost way to increase your referrals: Before you deliver a solution, tell your client that you prefer getting new business by referral. Less money spent on advertising means better deals for clients like him/her, and you’d like to work with more people like him/her. Ask them, “after we’ve delivered this and you are thrilled with how things work, would you refer us to your friends/colleagues?” After you’ve delivered, make sure they are thrilled, and only then ask for a list of friends or colleagues who would want the same service and expertise.