If relevant, why not annually wish your clients a happy birthday or anniversary (and perhaps include a special offer)?
- For letters, enter the date onto an Excel spreadsheet along with the mailing details. Sort the list each month and do a mail merge to those with current birthdays.
- Create a recurring Task in Outlook (or To Do in Lotus) that will pop up once every year.
You can immediately email that person a happy birthday. You go to genius status when you create a signature and insert that in the body of the email. The only work you do is type their name and a subject line.