I recently had a project to help spec out a DLP project for a customer from a high-level perspective. Having never done anything with DLP previously I embarked on a research mission. What I found was interesting. There's not much out there on the intarwebs. As such, I thought I'd offer a few quick suggestions, just in case you want to go research solutions, too.
1) Start with Securosis! Their reports are freely available, comprehensive, and more informative than anything else I found.
2) Search for Gartner and Forrester reports. While these analyst firms charge for their reports, vendors will often post them for free. Specifically, try these search strings:
---> forrester wave content security suites
---> gartner magic quadrant data loss prevention
3) Beware DLP (as in Digital Light Processing) from Texas Instruments. You might need to use advanced search functions to -television -TI and so on.
Happy hunting!