I've got to ditto Gerard's recommendation of Outlook. I've tried RE-oriented systems (TopProducer and clones) and other general contact management programs (GoldMine and clones). The best thing about Outlook is that you can configure it any way you want. The Business Contact Manager that comes with it allows you to track clients, projects and marketing campaigns. If you want to expand further, you can use Microsoft OneNote to assemble contact info, letters, notes, and other stuff into one handy folder. I'm using OneNote to store entire transaction files so that I don't have to dig the paper files out of storage when a question comes up about a past transaction (disclaimer: the OneNote electronic file doesn't meet the electronic format requirement for storage of files subject to state audits, so I keep the hard copies nearby).