The downside to Global Velocity is that it comes with just a few pre-set data types, although they are adding new ones continually. The ability to actually block data is still a beta feature but should be in the product by October. They also don't have any mechanism for handling encrypted data, but are working on that too.
Finally, there is BlueCoat's DLP solution. It comes with lots of pre-set data types, such as social security or credit card accounts, along with dozens of different policy templates. Your policy can be set up to allow, report, or block the particular action, and the product even has customizable block messages too. The BlueCoat DLP product is based on the CodeGreen engine and can work with BlueCoat's Proxy SG server to decrypt and classify messages. It contains policies to handle both inbound and outbound traffic on a variety of protocols and to examine Webmail and FTP traffic as well as standard email and Web.
Both BlueCoat's and Sendmail's devices can be setup to automatically encrypt messages that have sensitive information before they leave your domain. That is a nice touch and something that might get more people into using encrypted emails for these conversations.
As you can see, there is a lot under the covers that make these DLP products work. Understanding how they fit in with what security devices you already have, such as an email server or a firewall, will be the first step in evaluating which one will make the most sense for your particular needs.