I live and die by Salesforce.com, which has a $99/year option. It can be as complicated and custom as you want, but it also works really well without any customizations right from the start. What's nice is if you do find you need a particular custom field or report (say, people's Twitter handles, with another field that automatically makes a link to click and go to their profile), it takes two minutes to setup. I prefer this over less-customizable solutions that force me to work within their framework.
I have also heard good things about BatchBook (http://www.batchblue.com/) but haven't tried it myself. It's said to be a simpler contact-management solution but still customizable.