I have a great recommendation about this, actually! I use an online web app called "Highrise." I became addicted to it during my days as a software developer (I also used it's sister application, Basecamp, for project management). It is *fantastic* for contact management, task management, custom order management (they are called "deals") and much more.
It helps you manage all of your contacts, when you need to follow up with people, sending out email newsletters (for instance, export all "customers" for an email newsletter blast), and quick views of how many open sales you have, how many custom orders you're working on - how much they cost - and what you've promised.
Here's one of my favorite things. You can keep ALL correspondence in there (notes from phone calls, or copied and pasted directly from emails), including uploaded files and images, that relate to both contacts and/or specific sales. Better yet, they give you your own special email address and if you BCC any message to that address, it will put that particular message right into highrise for you!
It's SO handy. There's a free version, and up from there. I couldn't keep my head on straight without it. I'm happy to answer questions if people have them - I have a lot of karma to pay back for the critiques everyone has been helping me with my store :-)
Here's the URL:
www.highrisehq.com