I tried Prophet and liked the software but stopped using in because it didn't sync with Windows Mobile.

I've been using Microsoft's Business Contact Manager for about a year and it works well. I've got about 4,300 unique live contacts. It doesn't integrate with Windows Mobile that well either, but at least there's some integration.

When setting up a new contact I recommend setting it up in Contacts, dragging it to BCM (which will (unfortunately remove it from Contacts), and then dragging it back to Contacts.