Two more to throw in the ring.
It's not free, but it's a great program that will send you an appointment attachment for Outlook. It's
http://www.appointmentquest.com. This allows clients to schedule themselves into your calendar. I use it to have potential clients pick a time for their appointments. You just add a link to your website and they schedule themselves in. You also trap their contact information.
If your client also is into online networking, Plaxo (
http://www.plaxo.com) is an awesome online calendar system that (for free) will sync with Outlook. I think you have to upgrade to sync with your Blackberry, but you can sync with just about anything using Plaxo. AND they have a social network they are building that allows you to share your contact information with other business people. Fun and very beneficial.
Create a great day!
Kristen